OCR Text |
Show ERA OF THE OOLITE strata of themselves. The crinoidea and echinites were also extremely numerous. Shell mollusks, in hundreds of new species, occupied the bottoms of the seas of those ao·es, while of the swimming shell-fish, ammonites, and belemnites, there were also many scores of varietic'3. The belemnite hel'e calls for some particular notice. It cmn·· mences in lhe oolite, and terminates in the next formation. It is an elongated, conical shell, terminating in a point, and having, at the larger end, a cavity for the residence of the animal, with a series of air-chambers ,below. The animal, placed in the upper cavity, could raise or depress itaelf in the water at pleasure by a pneumatic operation upon the entral air tube pervading its shell. Its tentacula, sent abroad over the summit of the shell, searched the sea for prey. The creature hall an ink-bag, with which it could muddle the water around it, to protect itself from more powerful animals, and strange to say, this has been found so well preserved that an artist has u ed it in one in tanre as a paint, 'vherewith to delin ate the b lemnite itself. The cru tacea discov red in this formation arc less numerou . There are many fbhe , . orne of which (rzcrodus, 1J ammodus, &c.,) al'e presumed from remains of their palatal bones, to have been of the gigantic cartilaginous clas , now represented by such as the cestraceon. It .has been con idered by Prufe sor Owen a worthy of notice, that, the ce. traceon being an inhabitant of the Austrilian seas, \Ve have, in both the botany and ichthyology of this p riod, an analogy to that continent. The pycnodontes (thick-toothed) and lepidoide , (havin~ thick srales,) are other famili )s de cribcd by M. A~a 'iz as extensively pr val nt. 1 n the shallow wa t rs of the oolitic formati?n, the i ·hthyo ·auru., pl io auru , and other huge saunan carnivora of the prccPding age, pl1 d, in increased numbers, their d :tt'ncti v vocation.* To them were added u ·w u •n •ra, th · ·tio:auru ', mo ·o aurus, and some others, all of 'imilar ·hantcter and habit . lAnd r •ptiles abouncleri, incluclina.specie. of the pterodactyle of th prec: •ding a1r -tort01 'es, tnonyces croco- " In om instanC(!<l, th c::c fo<: ' ils arefonnd ":ith !he contents of th stomuch faithfully prt:s rn•cl, and P\' ('n w1th piCces of the e~ ternal . 1 in. The pell ·ts •jcclecl by th ·m (coprolites) are found m va t nurnh~rs, (•nch g<•nernlly enclosPcl in a noclule ironstone, an.d sometimes, howing remain of the fi hes wh1eh had forJxlCd thcu food. COMMENCEMENT OF MAMMALIA. dilians-and the pliosanrns, a creature which appears to have formed a link between the plesiosaurus and the crocodile. We know of at l0ast six species of the flying saurian, the pterod~ctyle, in this formation. Now, for the first time, we find remains of insects, an order of animals not well calculated for fossil preservation, and which are therefore amongst the rarest of the animal tribes found in rocks, though they are the most numerous of allli ving families A single libellula (dragon-fly) was found in the Stonefield slate, a member of the lower oolitic group quarried near Oxford; and this was for several years the only specimen known to exist so early : but now many species have been found in a correspondjng rock at Solenhofen, in Germany. It is remarkable, that the remains of insects are found most plentifully near the remains of pterodactyles, to which undoubtedly they served as prey. The first glimpse of the highest class of the vertebrate sub-kingdom-mammalia-is obtained from the Stonesfield slate, where there has been found the jaw-bone of a quadruped evidently insectivorous, and inferred, from peculiarities in the structure of that small fragment to have belonged to the marsupial family, (pouched animals.) It may be observed. although no specimens of so high a class of animals as mammalia are found earlier, such may nevertheless have existed: the defect may be in our not havino- found them; but, other things considered, the pro- ~ . bability is. that heretofore there were no mamm1fers. It is an interesting circumstance, that the first mammifers found should have belonged to the marsupialia, when the place of that order in the scale o!' cre~tion is ?onsi<;Iered. In the imperfect structure of their brain, deficient In the 01·o-ans connecting the two hemispheres-and in the mode ol' gestation, which is only in small J?a'tt uterine-this family is clearly a link betweer. the o~1parous verte~rata (birds, reptiles, and fishes) and the higher mammifers. This is further established by their possessing a faint develop went of two canals pa.ssing from. near the anus to the external surface of the viscera, wh1ch are fully possessed in reptiles and fishes, tor the purpose of supplying aerated water to the blood circulating in particular vessels, but which are unneerled by mammifers. Such rudiments of organs in certain species which do not require them in any degree, are cumnwn in both the animal and vegetable |