PACKARD. A NEW FOSSIL CRAB. 7 



lar to G. irroratus in the shape of the nine teeth on the antero-lateral 

 margin of the carapace, and in the straight postero-lateral margin of the 

 same. It is rounder, narrower, the carapace more convex, and the body 

 in general more hairy than either of the existing species. 



It thus seems most probable that the miocene species, being a more 

 generalized, composite form, is the ancestor from which either towards 

 the end of the pliocene or the beginning of the quaternary period the two 

 living species sprang. G. irroratus has inherited the exact shape of the 

 lateral teeth, and the shape of the postero-lateral margin of G.proavitus, 

 while G. borealis has retained the higher spine-like granulations or sub- 

 muricate feature of the carapace and hand, and the hairiness of the body. 



On the whole the evidence that our two northeastern species have de- 

 scended from a much more rounded, convex, and hairy miocene form liv- 

 ing in the same geographical area seems well established. 



It would be most interesting to compare this fossil species with very 

 young individuals of our living species, but after inquiry I find they 

 are not in existence in our museums. It is to be hoped that specimens 

 of the very young may be collected and compared with the fossil species. 

 It is known that in Cancer the body grows wider with age. 



Note on Archaeoplax signifera Stimpson.* — While the collections 

 of the fossil Crustacea made at Gay Head comprise only one speci- 

 men of Cancer proavitus, with the hand of a much larger individual, the 

 fragmentary remains of the Archreoplax are much more abundant, 

 showing that it was the most prevalent form. 



The specimens, however, in the Museum of Brown University, and 

 those collected by Mr. Clarke, and those in the Cambridge Museum, are, 

 so far as we have observed them, not sufficiently well preserved to enable 

 one to make a restoration which would be a very decided improvement 

 on the excellent diagrammatic drawings by Dr. Stimpson. None of the 

 specimens of the carapace — and in two large specimens they are tolerably 

 well preserved — show the four teeth of the antero-lateral margin; on 

 the other hand, in Mr. Clarke's specimens the legs of the four posterior 

 pairs are well enough preserved to show five of the joints, the terminal 

 ones wanting; the fourth joints are of unusual length. 



In one young specimen the carapace has been broken away on the 

 back so as to still show the gills in place. 



Regarding the temperature of the water of the miocene period at Gay 



* On the fossil C»ab of Gay Head, Boston Journal of Natural History, VII. No. 

 4, April, 1863. 



