264 Mr. R. I. Pocock on the Taxonomy 



Borneo, wliere presumnhly they exist side by side. These 

 specimens, the largest I have seen, measuring about 17 inches 

 lone:, cxcludinij tlic postanal spine, which sujicradds another 

 19 inches, were presented by Mr. G. \V. Johnstone and 

 Capt. S. S. Flower. 



Tachr/phus Iloevem, sp. n. (PI. V. fif^. D.) 



Limuhis mohiccnnus, Van der Iloovon, Kech. sur I'llist. n.at. etc. des 

 Liiindes, pp. 9 2G & 31, pi. i. figs. 2 & 10, pi. ii. fig. 14 (not pi. ii. 

 fig. 15). 



Van der Iloeven's figures of the species he identifies as 

 L. vioJuccanus are most puzzling. The genital operculum of 

 both male and female of his specimens, it we are to trust the 

 artist who figured it, is quite different from those of all the 

 specimens of Tachypleus known to me. In the description 

 Van der Hoeven contents himself with saying that the genital 

 operculum has a median fissure in its posterior part [loc. cit, 

 p. 15) ; but the admirable illustrations cited above clearly show 

 that the distal segments of tlie inner branch of this appendage 

 are disunited in the middle line, with their inner borders 

 sinuous and overlapping. Plate i. fig. 2 of his monograph 

 represents this arrangement in a female which is shown to be 

 adult by the abbreviation of the three posterior spines on the 

 opisthosoma, and plate i. fig. 10 and [)late ii. fig. 14 show 

 precisely the same thing in the adult male. The variation is 

 clearly therefore attributable neither to sex nor age, and its 

 occurrence in at least two specimens precludes the likelihood 

 ot its being due to abnormal development. 



That Van der Hoeven also had a specimen with the oper- 

 culum resembling that of the species I call gigas is indicated 

 by fig. 15, pi. ii., where this appendage is represented in its 

 typical form. Under these circumstances there appears to be 

 no other course than to regard the two types of operculum 

 as belonging to distinct species. In other characters, so far as 

 can be judged, the species appear to be alike. 



Jjistributiun. Moluccas. 



The distinguishing features of the three species referred to 

 this genus may be tabulated as follows : — 



a. Anterior border of carapace of ^ strongly bi- 



excised ; posterior margin of opistliosouia above 

 tlie root of the postanal spine armed witli 

 three spikes (ridoitatiiSj Leach. 



b. Anterior border of carapace evenly convex in J 



and $ ; caudal emargination of o|)isthosoma 

 armed above with a single median spike. 



