b PROCEEDINGS OF TEE AMERICAN ACADEMY. 



Survey with that of a ( Irroratus about four inches wide, notable 



are to be Been Though the four ridges are the Bame in length, 

 width apart, and in general arrangement, the teeth on these ridges are 

 in C. i much larger, and are represented in 0. irroratus 



by more numerous and crowded granulations, which are flattened, 



ind« d. and polished. 



In Borne important respects the tertiary species resembles O.bon 

 This differs from C irroratus in being finely moricate, the minute 

 iua tobercles being much larger, higher, and sharper, almost form- 

 sharp spines; they are also more numerous and crowded, and often 

 bear a hair. In these respects C. prottvittu approaches 0. borealis. As 

 in O. irrt the anterolateral margins are nine-toothed; of these 



b the ninth, or that m-xt to the orbit, is sharper than in the other 

 living and ends in a sharp Bpine, with several accessory spin ales, 



The postero-lateral margins are more sinuous than in C. irroratus, and 

 the granulations on the ridge are larger, fewer, and end in a point. In 

 both of tlu; Living species the convexity of the carapace is about the 

 Bame. The surface in 0. borealis is perhaps a little more uneven. 



The hand of C borealis differs from that of 0. irroratus in being 

 inueh more imiricatc or spiny, the granulations on the four external 

 ridges of the latter being represented by well-marked Bharp Bpines, these 

 being especially large and high on the uppermost rid_ 



( . borealis is a decidedly hairy species, whereas C. irroratus is 

 naked, but a few hairs being visible; on the other hand, in C. borealis 

 nearly every tubercle bears a pale hair. 



The abdomen of C. borealis differs from that of the more common 

 (<'. irroratus) in being less acute and mucronate at the tip. 



The sternum i- a little more hairy. 



jth of a Bmall C. borealis, 80 mm. ; breadth. 89 mm.; thickness 

 of l.oip . 10—11 mm. 



The phylogeny of the Eastern American species of the genus 

 Cancer. — A comparison of the miocene tertiary species of Cancer with 



the tWO Bpeciel now living in the waters of Vineyard Sound, brings OUl 



the interesting fad that the extinct Bpecies appears to be the stem or 



■ d form from which the recent Bpecies mentioned have descended. 



' ineer proavitus presents characters in which it resembles C.bore- 



i w.ll as c. irroratus. It resembles C. borealis in the higher, 



e pointed granulations on the postero-lateral margin of the carapace, 



in the <|uite high and Bharp Bpines on the ridges ol the hand, as well 



in - and hail-, ; 00 the other hand it i.-, .dmi- 



