OCR Text |
Show 1890.] OF THE FAMTLY BUTHIDCE. 117 denticles, all the arrangements met with throughout the family are easily derivable. The first modification that presents itself results from the assumption of an obliquely transverse position by the posterior tooth or two posterior teeth of each row. Thus arises the " external series " of Dr. Thorell. The internal series results, I believe, from the separation of the anterior tooth of each series from the rest ; this separation is sometimes carried to such an extent that all connection between the tooth and the series from which it arose is lost. If this view as to the original disposition of the denticles is correct, the arrangement seen in some species of lsometrus is that which comes nearest to the primitive plan. Thus in, e. g., Lmessor1 the anterior tooth of each series is enlarged, but not isolated, and the posterior tooth has altered its position, so that with that which precedes it it forms a transversely set pair ; in /. insignis the anterior tooth, although still in the same straight line with the rest of the series, is separated by a measurable interval from it, and in Lepreus fischeri the anterior tooth has shifted so much forwards that it is on a level with the anterior end of the row in front of the one from which it originated. Genus LEPREUS, Thorell. (Plate XIV. figs. 2-4.) Lepreus, Thorell, Etudes Scorpiol. p. 8. Hab. S.Africa. Immovable digit of chelicerae unarmed beneath. The external series of teeth on the chelae is formed by the bending outwards in a direction nearly at right angles to the axis of the digit of the two or three posterior terminal teeth of the median rows ; the internal series by the separation (greater or less, as the case may be) of the anterior terminal tooth. The cephalothorax is not distinctly keeled ; the tergites always have one median keel, and in a few cases two lateral short keels ; the caudal keels may be well developed or absent, and there may or may not be a spine beneath the aculeus. The tibiae of the two posterior legs are spurred. The basal pectinal tooth in the female is (? always) enlarged. In the arrangements of the denticles on the chelae the species of this genus vary considerably. Thus in L. fischeri, var. nigrimanus, all the teeth of the internal series have moved so far forwards that each is on a level with the anterior extremities of the row distal to the one from which it originated. Whereas, in specimens of L. occidentalis, at the proximal end of the digit each of the separated teeth is about equidistant from the anterior end of its original series and from the corresponding end of the series distal to this last; but in the middle and distal half of the digit each tooth moves forward and approaches close to the anterior extremity of the series distal to the one to which 1 I have no object in selecting this species; it happens to be the first that comes to hand. |