OCR Text |
Show 1890.] OF THE FAMILY BUTHIDCE. 121 The genus is common in America, and appears to have been derived from the American species of lsometrus; since all the specimens of Centrums that I have examined agree with all the American species of lsometrus, and differ from all the Buthidae of the Old World1, in possessing no spur at the extremity of the tibial segments in the last two pairs of legs. The male may generally be recognized by having a much longer tail than the female. 1 look upon Rhopalurus as synonymous with Centrums for the same reasons that have led me to consider Phassus as a synonym of lsometrus. The type of the genus, R. laticaudu, of which the Museum possesses examples of both sexes from Brazil and Colombia, does not appear to me to be other than a well-marked species of Centrums, standing in almost exactly the same relation to C. biaculeatus as /. americanus to I. androcottoides. So that if I. americanus be congeneric, as will hardly be disputed, with 1. androcottoides, then must R. laticauda be congeneric with C. biaculeatus. Genus BUTHEOLUS, Simon. Orlhodactylus, Karsch, Berl. ent. Zeits. xxv. p. 90 (1881) (uom. praeocc.) \ Butheolus, Simon, Ann. Mus. Genov. xviii. p. 258 (1882). Hab. Mediterranean district of Palaearctic Region. This is a genus of very doubtful affinities and is correspondingly hard to locate, inasmuch as it appears to partake of the characters of lsometrus, lsometroides, and Buthus. In his diagnosis of it M. Simon says that the inferior border of both the movable and immovable digits of the chelicerae are furnished with only one tooth; but this is by no means always the case, for in one of the specimens of B. melanurus 3 preserved in the National Museum there are the normal number, namely, two teeth on this edge in the movable digit and also, which is a significant fact, two teeth on the corresponding edge in the immovable digit as in Buthus. This, although probably an abnormal development, serves to lessen considerably the hiatus between lsometrus and Buthus, and to diminish the systematic value that has been placed upon the presence or absence of these teeth. The features in which this genus resembles lsometroides, namely the slender and unarmed vesicle, the punctured keelless fifth caudal segment, and the feeble chelae, are, considering the distribution of the two, in all probability not due to affinity between the genera, but have arisen independently in the two localities. lsometroides is much more nearly related to lsometrus thau is Butheolus ; the latter may be distinguished fromboth by the form of the cephalothorax, which is much sloped in front of the eyes and has a convex anterior border. The arrangement of denticles on the digits of the chelae is very simple in B. melanurus3; in the proximal half of the digit the median 1 With the e.xception of L. assameusis, melanophysa, and the cosmopolitan L maculatus. 2 Vide Simon, Verb. z.-b. Ges. Wien, xxxix. 1889, p. 386. 3 Kessler, Trudui Eusskago Entomol. viii. (1876), p. 16, pi. i. figs. 1-3 (= schncideri, L. Koch, &c). |