78 The American Geologist. February, isg4 
ventral surface exposed, shows some specific details which 
were invisible in the former. 
In the specific description the leading points of difference 
and those on which the definition rests are the greater size of 
the fossil and the smaller number of cusps or branches on the 
four anterior pairs of gnathopods. 
The specimen measures twenty-four inches in length, 
whereas none of those from which the description of C. new- 
lini was compiled exceeded fourteen. There are also only 
three cusps on the front edge of the first, third and fourth 
pairs of gnathopods. and four on the second pair. In ('. newlini 
these cusps are sometimes eight to twelve in number, and ap- 
parently in some cases project from the back of that organ, 
though this must be considered uncertain and against analogy. 
There is, moreover, on the large paddles no trace of the 
fringed or serrated edges* which are so conspicuous in the 
paddles of C. newlini. They are perfectly even and smooth. 
There are also some marginal projections on the hinder part 
of the cephalo-thorax which may be the traces of abdominal 
appendages, or they may be merely the projecting margins of 
their corresponding somites, jutting out beyond the general 
line of the body. 
No markings of any kind can be made out on the surface of 
the bod} 7 such as the crescentic sculpture on the carapace of 
Eurypterus. This may, however, be due to the roughness of 
the limestone matrix. 
The genus Carcinosoma appears to be- intermediate among 
several of the other previously known genera of crustaceans 
from this horizon. It has the long, spiny tail of Stylonurus 
and its branched gnathopods, the large fifth pair of append- 
ages of Pterygotus, the wide, short body of Limulus or of the 
limuloids of that time, and the four small anterior pairs of 
appendages of Puryptei us. Its nearest ally is apparently 
Kusarcusf of Grote and Pitt, described in the Bulletin of the 
Society of Natural Sciences (Vol.. in, No. 1 ). Hut the descrip- 
tion of that genus mentions that the cephalo-thoracic portion 
*Misprinted '•eyes'' in the original description, p. 260, American Ge- 
ologist, 1890. 
tin Miller's Catalogue of Palaeozoic Fossils this is put down as a syn- 
onym of Eurypterus, but the distinctions are quite sufficient to warrant 
generic separation. 
