24 Annals of the South African Museum. 



GEN. DIOGENES, Dana. 



1852. Diogenes, Dana, U.S. Expl. Exp., Crust., vol. xiii., pt. 1, 



pp. 435, 438. 

 1905. Diogenes, Alcock, Indian Decapod Crust., pt. 2, pp. 25, 59, 



164. 



Dana gave the following definition : " Ophthalmic ring bearing a 

 rostrum. Fourth pair of feet subcheliform. Left hand the larger; 

 fingers acuminate, calcareous at tips." He distinguished this genus 

 and Eupagurus (which he called Bernhardus] from Paguristes by the 

 character that they were without appendages behind the bases of 

 the fifth leg, whereas such appendages are present in Paguristes. 



DIOGENES COSTATUS, Henderson. 



1893. Diogenes costatus, Henderson, Tr. Linn. Soc. London, Zool., 

 Ser. 2, vol. v., pt. 10, p. 418, pi. 39, figs. 7, 8. 



1905. Diogenes costatus, Alcock, Indian Decapod Crust. ,pt. 2, pp. 61, 

 70, pi. 6, figs. 7, la. 



The present species belongs to the group in which " the rostrum 

 is a slender simple (non-serrated) spicule " (Alcock). It appears to 

 be very nearly allied to D. pugilator (Roux), known in the south of 

 England as well as the Mediterranean and elsewhere, and to the 

 oriental D. avarus, Heller. But the last species has a much more 

 narrowly elongate left cheliped. 



In the specimen here attributed to D. costatus the carapace has 

 the antero-lateral margins serrulate, the rostrum shorter than the 

 subtriangular spinulose ophthalmic scales, the antennal acicle a 

 simple spine, strongly spinose along the inner edge, but differing 

 from the figures in Henderson and Alcock by having a denticle on 

 its outer edge. In describing the left cheliped Alcock says " merus 

 a little shorter than the carpus," the reverse of which is the case in 

 his figure and in our specimen. Both he and Henderson lay stress 

 on the fact that the outer surface of the palm " is traversed by a 

 ridge which, beginning at the lower proximal angle, runs up parallel 

 with the carpal articulation (where it is granular), and then curves 

 round and is continued obliquely almost to the finger-cleft " (Alcock). 

 They do not refer to what is shown in their figures, the fact that the 

 fixed finger has on its inner margin a marked prominence fitting a 

 corresponding cavity in the inner margin of the movable finger. 

 The little right cheliped shows a considerable gap in the closure of 

 the setose hand and finger. 



