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 



nt 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. 



Dimensions. 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 Mesothi/ra Neptuni probably the largest known 

 species of the genus. 



Observations. The specimen upon which the original description of this 

 cies 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 i.- accompanied by more or less fragmentary impressions of four similar 

 i lal parts and a fragment of the marginal portion of one valve of the cara- 

 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- 

 nnlu.s Dekayi and is thus beyond doubt from the Hamilton beds. 



I i '1,.. preliminary illustration of the New York Devonian Crustacea (Illus- 

 trations of Devonian Fossils, he. 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 

 aterial a careful comparison of the specimens from the two localities has 

 hown that those from the Portage group present many well-marked and 

 ml specific features distinguishing them from the type of Dithyrocaris 

 This latter species must therefore be considered as limited to the 

 'Iton fauna, and our knowledge of it is thus far confined to the specimens 

 from which the original description was drawn. 



Hamilton .roup. From a loose block in the town of Plain- 

 field, ' i countj . 



