OCR Text |
Show 78 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. specimen. Mr. Darwin took it at Maldonad.o, wher~ he states that it is very common, adding that it is sometimes found m brackish water. M. D'Orbigny had also found it previously at the mouth of the Rio Plata. 2. ATHERINA MICROLEPIDOTA. Jen. PLATE XVI. Fig. 1. Nat. size. Fig. 2. a, b. :Magnified scales. A. gracilis; corporis altitudine partem octavam, capite quintam, longitudinis cequante: oculis medioC'ribus: maxillis sub-cequalibus, parum protractilibus; commissw ·a primum ltorizontali, deinde paulo deflexa, !laud oculos attingente : dentibus velutinis, serie externa supra s?tbtusquefortiori: do1·sali prima omnino pone ventrales 1·eclinatas locatd: squamis parvis, seriebus longitudinalibus octodecim ad minimum dispositis. D. 5-1/11; A. 1/17; C. 17, &c. P. 15; V. 1J5. LoNG. unc. 4. FoRM-More slender and elongated than the generality of the species in this genus. Greatest depth not more than one-eighth of the entire length. Head one-fifth of the same. Greatest thickness (in the region of the gills) equalling two-thirds of the depth, or rather more. Ventral line of the body scarcely more curved than the dorsal. The upper profile falls, though very slightly, from the nape to the mouth, and the lower profile inclines upwards to meet it at about the same degree of curvature. Head broad, its breadth across the crown nearly equalling its depth. Snout horizontally rounded. Jaws nearly equal; not so protractile as in some other species: the commissure of the lips at first horizontal, but postel'iorly inclining a little downward, and scarcely reaching more than half-way to the eye. In each jaw two rows of slender very distinct teeth, with traces of a third or even fourth row above, towards the middle: outer row longest and most conspicuous, consisting, in the uppet· jaw, of from fortyfive to fifty teeth ; in the lower of scarcely more than twenty-five. No teeth that can be seen on the vomer or palatines, though a slight roughness can be felt on both. Eyes of moderate size; their diameter rather more than one-fourth the length of the head ; almoE~t entirely before the middle, as well as above it: space between the eyes flat, and exceeding the diameter by about one-third : a slightly elevated line on each side of this space, but no other conspicuous sculpture. Opercle with the descending margin sloping obliquely forwards. Crown, cheeks, and gill-covers scaly, the scales on the crown extending as far as the eyes. Scales on the body small, the number of longitudinal rows amounting to eighteen or twenty: in form nearly square, the length a little exceeding the breadth, the superficies marked with numerous very distinct concentric lines, the basal half with a fan of from four to six deeper cut strire, the basal margin rather sinuous, and obsoletely crenate where the strire meet it. No lateral line very distinguishable. First dorsal small and delicate, commencing exactly at the middle point of the entire length, measuring this last to the bottom of the caudal fork, and in a line with the tips of the ventrals, these last fins being laid back. Space between the first and second dorsals a little exceeding two thirds of the depth of the body. Length and height of the second dot-sal equal |