1890.] OK THE lAMILY BUTHID.E. ' 121 



The genus is common in America, and appears to liavc been 

 cleriyed from the American species of Isometrus ; since all the 

 specimens of Centrurus that I have examined agree with all the 

 American species of Isometrus, and differ from all the Buthidse ot 

 the Old World \ 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. I look upon llhopalurus as synonymous with 

 Centrunts for the same reasons that have led me to consider Phassus 

 as a synonym of Isometrus. The type of the genus, R. laticauda, 

 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 

 sjjccies of Centrurus, standing in almost exactly the same relatioi\ to 

 C. hiaculeatus as /. americanus to /. androcottoides. So that if /. 

 americttnus be congeneric, as will hardly be disputed, with 1. andro- 

 cottoides, then must R. laticauda be congeneric with C. biaculeatus. 



Genus Butheolus, Simon. 



Orthodactylus, Karsch, Berl. ent. Zeits. xxv, p. !J0 (1881) (uom. 

 j)rseocc.) '. 



Butheolus, Simon, Ann. Mus. Genov. xviii. p. 258 (1882). 



Hah. Mediterranean district of Palsearctic 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 Isometrus, Isometroides, and JButhus. In his diagnosis of it M. 

 Simon says that the inferior border of both the movable and immov- 

 able digits of the chelicerse are furnished with only one tooth ; but 

 this is by no means always the case, for in one of the specimens of 

 jB. melanurus ^ preserved in the National Museum there are the normal 

 number, namely, two teeth on this edge in tlie movable digit and also, 

 which is a significant I'act, 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 

 Isometrus and Buthus, and to diminish the systematic value tliat 

 has been placed upon the jjresence or absence of these teeth. The 

 features in which this genus resembles Isometroides, 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. Isometroides is 

 much more nearly related to Isometrus than is Butheolus ; the latter 

 may be distinguished from both by the formof thecephalothorax, 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. melanurus ^ ; in the proximal half of the digit the median 



* With the exception of /. assamoisis, nielanopki/sa, and the cosmopolitan 

 /. maculuhis. 



- ride Siiuoii, Xiii-h. z.-b. Gl's. Wiou, xssix. 1880, p. oSO. 



^ Kessler, Trudui Kii.sskugo Eiitomol. viii. (1S76), p. 1(5, pi. i. iigs. l-.j 

 (= iL/m.idcri, L. Ivocli, iLc). 



