PENNSYLVANIAN FOSSILS 



115 



Astartella (fig. 321) and the remaining genera are wingless. Astar - 

 t ella has a rounded shell with prominent beaks and numerous concentric 

 ridges; the latter feature distinguishes it from Nucula. Six species of 

 Astartella have been recorded from Ohio. 



Nucula (fig. 322) is mentioned twice in the key as some species are 

 longer than high, others higher than long. The nature of the concentric orna- 

 mentation will distinguish this genus from Astartella and the absence of a 

 ridge from beak to margin separates it from Schizodus. Six species are 

 recorded as common from Ohio. 



Fig. 321 



Fig. 322 



Fig. 323 



Fig. 325 



Edmondia (fig. 323) is one of several genera with nearly central 

 beaks and a rounded outline. The widely spaced concentric ridges 

 separate it from Schizodus and Nucula . Six species of Edmondia are 

 recorded, several of them common. 



Schizodus (fig. 324) has large beaks and a strong 

 ridge running from the beak to the margin of the shell. 

 The outline varies from almost round to elongate. Seven 

 species, of which 3 are common, are recorded. 



Solenomorpha is a distant relative of the living Fig. 324 



razor clams. The elongate shell is distinctive. One species, S. 

 lamborni (fig. 325) is common. 



Parallelodon (fig. 326) is similar to the next two genera in having 

 an elongate shell with a strong ridge from beak to margin. It differs from 

 them in that the ridge is rounded and not keeled and in having low but 

 distinct radiating ridges on the entire shell or 

 part of it. Four species of Parallelodo n are 

 common in Ohio. 



Fig. 327 



Fig. 326 



Pleurophorella (fig. 327) is like Parallelodo n but has 3 distinct 

 radiating ridges and an otherwise unridged shell. Three species are 

 common. 



Pleurophorus (fig. 328) has 4 to 6 widely spaced radiating ridges on an 

 otherwise almost smooth shell. Three species are common. 



The shell of Nuculana (fig. 329) is pointed at one end; the concentric Fig. 328 



ornamentation of fine, sharp concentric ridges is like that of Nucula . Four species are 

 common. 



Allorisma terminale (fig. 330) can be recognized by the position of the 

 1 beaks which are almost at the end of the hinge. It is common in some beds. 



Fig. 329 



Cypricardinia has much the same shape as 

 Allorisma but the beaks are not at the end of the 

 hinge. C. carbonaria (fig. 331) is a common 

 species. 



Fig. 330 



GASTROPODA . Our Pennsyl- 

 vanian rocks contain an abundance 

 of gastropods belonging to many genera. We have 

 chosen only the commoner forms for discussion 

 here. The generic names used are those in the 

 most recent works we have been able to find and 



