ZOOLOGY. 
ccxxxvii 
of the modern genera ; as the object of the present account is limited to 
describing the new species in such manner, that systematic writers may be 
at no loss in disposing them according to their respective arrangements, 
the present species has been continued with the Crangons, Vulgaris, Bo- 
reas, and Spinosus, with which it accords so strikingly in general appear- 
ance, as well as in the leading and most essential characteristics ; with the 
reservation, however, of a notice, that it forms an exception to the “ pedes 
decern unguiculati” of the other Crangons. 
Alpheus Aculeatus. 
A. thoracis carina dentibus quatuor, margine antico trispinoso, segmentis utrinque aculeatis, palpis 
pediformibus apice spinulosis. 
Cancer Aculeatus O. Fabr,, Faun. Green., N°. 217. 
Astacus Groenlandicus, J. C. Fabr. Ent. Syst., Vol. 2., P. 484? 
Plate II, fig. 9, 10. 
Several individuals were . obtained at Melville Island, which being com- 
pared with the minute description of the Cancer Aculeatus of O. Fabricius, 
are believed to be the species described under that name : it is observable of 
this, as of other species of this genus, that the rostrum is found to vary so much 
in different specimens, in length and shape, as well as in the number of teeth 
above and below, as to make it no proper ground of specific distinction. 
It is probable that the Astacus Groenlandicus of J. C. Fabricius should also 
be referred to this species ; as, excepting the rostrum, the descriptions are 
sufficiently conformable, and the “ abdominis segmenta terminanter utrinque 
spin^,” of the Groenlandicus is strictly descriptive of the peculiar character- 
istic of the Aculeatus. It is possible also that the Astacus Histrio* of the 
same author, Ent. S^st., p. 482, may have been a young individual of the 
present species, since it appears to differ in colour only. 
* In the specific character of the Astacus Histrio, J. C. Fab. Ent. Syst. v. 2, p. 482, the margin 
of the thorax is said to be furnished with two teeth, whilst in the description which is added, the 
number of teeth are stated to be three; the former is presumed to be the error. 
2 g 2 
