86 Mr. C. Spence Bate on Nannastacus. 



Dr. Walker, who obtained it during Sir F. L. M'Clintock's last 

 Arctic expedition. It is preserved in the Dublin Museum. 



I take this to be the same as the smaller specimen figured 

 by Professor Thomas Bell in his account of the Arctic Crus- 

 tacea brought home by Sir Edward Belcher, and supposed by 

 him to be either a male or immature specimen of Diastylis 

 (Alauna) Goodsiri, although they " differ in some characters, as 

 the less convex form of the carapace, more obvious rugae on the 

 fore part of it, and the existence of an acute point on each side 

 of the last leg-bearing " somite. 



From this the specimen now described differs in such minute 

 points as may be only errors in figuring, or at most minor varia- 

 bility in individual character — as, for instance, the apparently less 

 regularity of the rows of small spines on the anterior surface of 

 the carapace, and the serrated condition of the antero- inferior 

 margin of the carapace. 



I must also allude to the remarkable circumstance of a second- 

 ary appendage being attached to the inferior pair of antennse in 

 this specimen, which I have never seen or known of its having 

 been observed in any of the genera. Undoubtedly it homo- 

 logizes with the squamiform appendage attached to the third 

 joint of the inferior antennse of the Macrurous Decapods, and 

 is consequently the homotype of the secondary appendage so 

 common to the superior antennae of Crustacea in all orders, and 

 to which in our present specimen it bears some considerable 

 resemblance. In the inferior antennse the peduncle normally 

 consists of five joints ; but in this the organ assimilates to the 

 character of the superior antennse. Thus we perceive that the 

 two joints usually existing beyond the secondary appendage are 

 here reduced to the condition of those inferior joints which we 

 describe as articuli. 



This condition of the antennse in this group of Crustacea 

 demonstrates very forcibly the depauperized character of the 

 animals — a circumstance that suggests the probable liability to 

 some more or less variation in those organs which have suffered 

 depreciation from the normal type, but are essential to the wel- 

 fare of the existence of the animal. It is under such considera- 

 tions as these that I am led to the belief that impoverished 

 appendages such as these antennse are can have but little dia- 

 gnostic importance in the determination of specific characters. 



Nannastacus*, nov. gen. 



The anterior somite of the carapace is separated from the 

 posterior by a distinct suture. The antero-lateral extremities of 



* Nawoy, dwarf; clo-tcikos, marine crab. 



