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Show 116 MR. R. I. POCOCK ON THE SCORPIONS [Mar. 18, the tibiae of the two posterior legs were armed with a spur ; the pectinal teeth were all alike ; the stigmata were slit-like. This diagnosis agrees more nearly with the plan of lsometrus than with that of any other genus, notwithstanding that there is in lsometrus a single lower tooth on the immovable digit of the chelicerse. lsometrus is cosmopolitan, and in Australia, Africa, and America it appears to have given rise to three distinct genera. In Australia fsometroides has sprung up through the loss of the spine beneath the aculeus and by the acquisition of coarse punctulation on the under surface of the fifth caudal segment; in America Centrums originated by the development of short rows of teeth connecting the extiemities of the median rows of the digits of the chelae ; in Africa Buthus arose when a second inferior tooth appeared behind the first on the immovable digit of the chelicerse. Beyond this stage Rhoptru-rus has not passed ; but Grosphus has lost a distinct spine beneath the aculeus, and in the female the basal pectinal tooth has become dilated. Parabuthus can be derived from Grosphus by a slight modification in the arrangement of the denticles on the chelae, by the loss of the enlarged pectinal tooth (perhaps through its fusion with the shaft of the pecten), and by an increase in the strength of the tail; whether Buthus (s. s.) has been derived by the development of lateral tergal keels from Parabuthus or Grosphus it is not easy to say; but that Prionurus has been developed from Buthus by an alteration in the form of the tail will probably not be disputed. Lepreus resembles Grosphus in possessing an enlarged basal pectinal tooth in the female; but whether this genus has been derived from Grosphus by the loss of the two lower teeth, and by a modification in the armature of the chela?, cannot as yet be settled. But inasmuch as the arrangement of the denticles on the chelae more nearly approaches in Lepreus than it does in Uroplectes what is met with in Grosphus or lsometrus, I consider that Uroplectes is a descendant of Lepreus. Butheolus is isolated, and may have been derived from either Buthus or lsometrus. Before proceeding to a consideration of the genera, it will be well to discuss shortly the armature of the digits of the chelae and the probable origin of the various modifications that are presented. Generally speaking, the dentition throughout the family may be described as consisting of a number of oblique, overlapping, parallel rows of fine close-set denticles. On each side of this median series there is a row of larger, more widely separated teeth, and the question to be decided in connection with these lateral teeth is whether they have been derived from the median rows or have arisen independently of them. However, after examining many genera and species of Scorpionidce as well as of Buthidce I am strongly inclined to believe that the lateral teeth have been derived from the median series, and that originally the armature of the chelae consisted solely of a number of oblique, overlapping, parallel rows of close-set denticles, and that perhaps one or two terminal denticles of each row were larger than the rest. From this relatively simple disposition of |
