192 
PALEONTOLOGY OF NEW YORK. 
tomosing striae, which are conspicuously angled over the median ridge of the 
caudal plate and pass thence backward over the lateral spines. They are 
absent upon the telson except near its base, and upon the cercopods are more 
abundant toward the outer edge, becoming obsolescent as they approach the 
extremities. 
Dimensimis. The caudal plate has a width of 27 mm.; the entire length of 
the caudal plate and telson is 81 mm. Each cercopod measures 110 mm. in 
length. 
The individual represented by the post-abdomens must have been of great 
size when entire, making Mesothyra Neptuni probably the largest known 
species of the genus. 
Observations. The specimen upon which the original description of this 
species was based is a very large caudal plate with the spines attached. It 
lies upon the surface of a slab of arenaceous shale, obtained in Otsego county, 
and is accompanied by more or less fragmentary impressions of four similar 
caudal parts and a fragment of the marginal portion of one valve of the cara¬ 
pace. Of the five impressions two are of the ventral and three of the dorsal 
surface, one of the latter being the type specimen and one a fragment of a con¬ 
siderably larger individual. The slab also bears a cephalon of a young Homalo- 
notus Dekayi and is thus beyond doubt from the Hamilton beds. 
In the preliminary illustration of the New York Devonian Crustacea (Illus¬ 
trations of Devonian Fossils, loc. cit.), a series of large carapaces and post-ab¬ 
domens from the lower beds of the Portage group at Ithaca, Tompkins county, 
were provisionally referred to the same species; in the final revision of this 
material a careful comparison of the specimens from the two localities has 
shown that those from the Portage group present many well-marked and 
constant specific features distinguishing them from the type of Dithjrocaris 
Neptuni. This latter species must therefore be considered as limited to the 
Hamilton fauna, and our knowledge of it is thus far confined to the specimens 
from which the original description was drawn. 
Distribution. Hamilton group. From a loose block in the town of Plain- 
field, Otsego county. 
