CRUSTACEA. 



95 



Sub-Class II.— Entomostraca. 



The Crustacean species which compose this division are usually 

 small and covered, partially or wholly, by a thin horny shell of bivalvu- 

 lar form. The absence of a series of abdominal appendages is the most 

 persistent characteristic. A few of the fossil Entomostracans are of 

 quite large size, but the majority are very minute and in such countless 

 numbers that they assist by their multitudinous atoms in building up 

 thick strata of the earth's crust. The larger and more highly organized 

 forms occur in the Palaeozoic Rocks. 



]No. 363. Dithyrocaris Neptuni, Hall. 



Caudal Spines. This large Phyllopodous Crustacean had a naked body, 

 or only the head and thorax covered by the carapace ; foliaceous and gill-bearing 

 limbs, serving as respiratory and natatory organs, and numerous feet. Its tail 

 was armed by a very conspicuous trifid spine. Hamilton Group (Devonian), Otse- 

 go Co., N. Y. 



No. 364. Limuhis gigantens, Miinst. 



This ancient '•• King-Crab," like those of the present 

 day, was covered by a cephalo-thoraxshield ; the append- 

 ages were all oral ; and the eyes were sessile and placed 

 in the upper surface of the shield. It belongs to the 

 Crustacean order Pcecillopod, or those which have the feet 

 of different segments of the body applied to different 

 uses. This fine specimen is from the Lithographic lime- 

 stone (Upper Oolite) of Eichstadt, Bavaria.. 



Size, 20 x 12. Price, $3.00. 



No. 365. Limuhis Walchii, Desm. 



A slab which shows the specimen both in impression and in relief. From 

 the same locality as the preceding, and now in the private Geological Cabinet of 

 Mr. Ward, Rochester. Size, 10 x 6. Price, $2.00. 



No. 366. Limuhis "Walchii, Desm. 

 From the same locality as the preceding 



Size, 7x5. Price, $0.60. 



No s 367. EurypteniS lacustris, Harlan. 



The genus Eurypterus— the Idotea of Scouler— was established by De Kay 

 in 1825. The name is an allusion to the broad, oar-like, swimming feet. The 

 body is composed of an anterior oval carapace, six thoracic and six abdominal 

 segments, and a somewhat obtuse tail-spine. The eyes were on the surface of 

 the carapace. There were five pairs of appendages, all oral, of which the hinder 



