REPORT ON THE CRUSTACEA MACRURA. 141 



The flagella of the antennae as well as the structure of the peduncles correspond in 

 the two specimens, and there is no important variation in the structure of the 

 appendages of the mouth. 



The first pair of pereiopoda is imperfect, but the meros is armed -with two small teeth 

 on the outer and two on the inner margins, which last differ from those in the male 

 specimeu. 



The other pairs correspond, but the posterior pair has the last joint broken off. 



The specimen, as I before said, is imperfect. Besides the fingers of the large pair of 

 claws the posterior pair of pereiopoda is only perfect as far as the propodos, and there is 

 no evidence to determine the character of the appendages in this specimen, which is 

 undoubtedly a female, the vulva being visible on the third pair of pereiopoda, 



The first pair of pleopoda is small, slender, and feeble ; the second pair carries 

 but a single stylarnblys. This specimen was taken at half the depth of the preceding, 

 at a temperature of 43°, on a bottom of volcanic mud. 



The branchial arrangement corresponds with that of Pentacheles in the delicate 

 character of the mastigobranchia, which is of great tenuity and shorter than the plume 

 with which it is associated. 



It will be interesting to compare with this species that which is described by Smith 

 as Polycheles sculptus, 1 and with Pentacheles sculptus, 2 and Pentacheles spinosa* 

 of A. Mdne-Edwards. 



Professor A. Milne-Edwards' description is short and agrees with Polycheles helleri 

 in every point mentioned. But Mr. Sidney Smith's description is more complete and is 

 fully illustrated by good figures of the entire animal in both dorsal and ventral aspects, 

 as also of most parts in detail. After studying the paper and figures carefully I can detect 

 no distinction of sufficient importance to separate Pentacheles sculptus from Polycheles 

 helleri, nor would it have taken much consideration to decide their identity had it not 

 been for the generic character of the fifth pair of pereiopoda, and that the specimens were 

 procured from localities so widely apart. Polycheles helleri lives in the Eastern Pacific at 

 depths of from 500 to 1000 fathoms, and Pentacheles sculptus in the Western Atlantic, 

 at about 600 fathoms. 



It is highly probable that many of the animals that we determine as specifically 

 distinct, because they are found in widely separated localities, and exhibit some greater 

 or less deviation from each other, would cease to be considered such if they lived side 

 by side, and there can, I think, be little doubt that many of our museum specimens are 

 not really species. 



A comparative examination of the Atlantic Pentacheles sculptus with that of the 

 Pacific Polycheles helleri, will elucidate clearly the point in question. 



1 Ann. ami Mag. Nat. Hut, ser. 5, vo'l. v. p. 269, 1880. 



-' Bull. Mus. Camp. Zool, vol. x. p. 23, pis. iii., iv., 1882. 3 Bull. Mus. Comp. Zool, vol. viii. p. 66, 1880. 



