CRUSTACEA FROM THE 'CHALLENGER' EXPEDITION.. 49 



exception of the right claw, are all densely covered with hairs. To three pairs there are 

 chelae ; the fourth has a small recurved claw at the end ; and in the fifth the sixth joint 

 is nothing but a very small stump. Very remarkable are the first pair of pereiopods ; the 

 chela of the right one has a length of 100 millims., and that of the left one of only 

 48. Between the two chelae, however, there is not only the difference in length, but 

 also in width, as the carpus in the right one is very much expanded, spiny, and 

 hairless ; in the left one it is even and covered with hairs and spines. The two digiti 

 chelae have large teeth at their inner side, 57 on the digitus mobilis, and 62 on the oppo- 

 site one ; so that the claws of the larger pereiopod look like the jaws of some ferocious 

 reptile. 



The genital openings are here at the base of the third pereiopod, where we also found 

 them in the male of Deidamia leptodactyla. 



Between the last pairs of pereiopods there is a small triangular pectoral plate. 



The pleon is very flat ; and the sharp angles formed by a longitudinal line on both 

 sides give it nearly a square shape. Its lateral pieces do not terminate in sharp spines, 

 nor are they very large ; the edges of these, as well as the whole surface of the third 

 and fourth segments, are covered by dense and short hairs. The telson is a square, as 

 it is in many Astaci ; its lateral appendages are very large, and extend, like wings, to 

 both sides. 



The pleopoda of the first, very short segment are styliform appendages ; the other 

 pleopods have a very solid unjointed base and two broad rami, the interior of which is 

 longer than the exterior (fig. 1 a). All these, as well as the caudal appendages, are 

 densely fringed with hairs. 



Characters of the Species. 



ASTACUS ZALBUCTJS, n. sp. 



Eyes and eyestalks wanting entirely. Chelae of the first pereiopod unequally developed, 

 the right one having more than double the length of the left one. Eight spines at the 

 squamiform appendage of the outer antenna. Genital opening of the male at the base of 

 the third pair of pereiopods. 



Those who consider the eyestalk an appendage of a separate segment of its own 

 would probably be inclined to make another genus of this form. But I think this could 

 be the only reason for separating it generically from Astacus, and for me not a sufficient 

 one. We find in Deidamia that the genital opening of the male is, in one species, at the 

 third pereiopod, and in another, undoubtedly belonging to the same genus, at the fifth. 

 I therefore think that also this cannot be a reason for separating it generically from 

 Astacus, in which genus this species will be the first one made known as an inhabitant of 

 the sea. 



To the Astacus of the Mammoth- cave this crayfish has only a physiological resem- 

 blance ; for even in those species in which the eyes are abortive the stalks at least are 

 present. But we have another form, which we got in deep water near the Bermudas, 

 in which the eyes have the same hidden position as in A. pellucidus, to which it has in 

 all other respects an extreme likeness ; only in the marine species the squamiform ap- 



SECOND SEEIES. — ZOOLOGY, VOL. I. H 



