PACKARD. — A NEW FOSSIL CRAB. 5 



On the posterior edge of the penultimate sternal segment are two 

 minute tubercles, but with the tips broken off, which are exactly as 

 in G. irroratus ; these little tubercles we take to be the "genital tuber- 

 cles " of Stimpson. The abdomen itself is wanting. The sternum is on 

 the whole rather more like that of G. borealis than G. irroratus. 



The large hand evidently belonging to this species is marked in 

 exactly the same manner on the outer aspect as in G. borealis, having the 

 four distinct raised granulated lines or ridges, with the same arrangement 

 as in the living species. The single specimen lacks the articular face at 

 the base, as also unfortunately the fingers, and also the spine at the base. 



Of the four ridges on the inner face, on the lowest ridge there 

 are 32 papillae, or conical granulations; on the ridge above, where 

 they are much smaller, about 33; in the third ridge there are two 

 rows of conical granulations, one consisting of 20 large ones, with 

 a parallel row of minute ones below; on the fourth ridge there are 

 about 12-14 large granulations, with smaller ones situated irregularly on 

 the lower side, while some others are interpolated between the large 

 ones. The concavities between the ridges are well marked. 



Length of carapace, 30 mm. ; width, 38 mm. 



Thickness of the body in the middle, 17-18 mm. ; amount of con- 

 vexity of the dorsal surface of the carapace, about 5 mm. 



Length of sternum, 20 mm. ; greatest breadth, 12 mm. 



Length of hand without the fingers, of the other specimen, 30 mm.; 

 breadth, 21 mm. 



On comparison with seven small G. irroratus (2 $ and 5 9 ) of nearly 

 the same age, it is seen to differ markedly in three points, i. e., the 

 very narrow, much rounded, or orbicular body, the much more convex 

 carapace, and the much greater number and prominence of the flattened 

 tuberosities. 



In the small G. irroratus 34 mm. long the carapace is 50 mm. in 

 width, or 16 mm. wider; in G. proavitus, which is 30 mm. long, it is 

 only 8 mm. wider than long. 



In G. irroratus we see only traces of the tuberosities on the sides of 

 the carapace, those of the median line being obsolete. On each side of 

 the median line or region in G. irroratus are tw.o obscurely marked 

 tuberosities, but they are very low, broad, and flat. The most striking 

 difference, however, is the much more rounded shape of the body. 

 On the other hand, the teeth and granulations on the teeth, and on the 

 narrow ridges of the posterior edge of the carapace, are nearly identical. 



Comparing the hand of the fossil species from the U. S. Geological 



