416 



MOLLUSCOIDEA 



PHYLUM V 



CharioneUa Billings. Similar to the last, but with a greatly modified 

 hinge-plate. Devonian ; North America. 



Pentagonia Cozzens {Goniocoelia Hall). Meristellids with a broad, angular, 



Fig. eSO. 



Meristina tumida (Dalm.). Silurian ; Gotland. A, Shell of the natural size. B, Interior of ventral valve. 



C, Hinge-line and median septum of dorsal valve. 



sharply limited, ventral sinus and abrupt lateral slopes. Dorsal valve with 

 a wide, rounded fold, divided by a narrow sinus and umbo-laterally with two 

 short flanges. Devonian ; North America. 



Merista Suess (Camarium Hall) (Fig. 631). Like Meristella, but with a 

 spondylium. Silurian (?) and Devonian ; Europe and North Amei'ica. 



D 



Fin. 631. 



Merista harculea (Barrande). Devonian (P"-) ; Konieprus, Bohemia. A, External aspect of ventral valve, 

 broken away near the apex so as to show the " shoe-lifter process," i/j. i>, Fractured shell showing median 

 septum ; spiralia destroyed (after Barrande). C, D, Frontal and lateral views of spiralia, slightly enlarged 

 (after Davidson). 



Dicaniara Hall and Clarke. Meristellids with a spondylium (" shoe-lifter 

 process ") and brachidium. Devonian ; Europe. 



Dioristella Bittner. Similar to Meristella. Alpine Trias. 



Camarospira Hall and Clarke. Like Meristella, but with a small spon- 

 dylium supported by a median septum, to which is attached only the pedicle 

 muscle. Devonian ; North America. 



Family 8. Ooelospiridae Hall and Clarke. 



Specialised Spiriferacea, with the primary lamellae as in the Meristellidae ; the 

 jiigum has a single process which may remain simple and free, or articulate in a 

 ventral septal socket. Shells plicate, often lainellose, and the strncttire impunctate. 

 Silurian and Devonian. 



Anoplotheca Sandb. (Bifida Davidson). Concavo-convex small shells with 



