462 



MOLLUSCA. 



318), of the Upper Cambrian, resembles Oboldla in many 

 respects, but possesses a straight hinge-line. 



Fig. 318. Kutorgina cingulata. (Billings.) Upper Cambrian. 



FAM. XI. TRIMERELLID^:. This, the last family of the 

 Brackiopoda, is related to the preceding, and comprises 

 forms in many respects allied to Obolibs. The shell is 

 inequivalve, calcareous, the beaks usually prominent, or 

 sometimes obtusely rounded, and either massive and solid, 

 or divided by a partition into two chambers. There is a 

 well-developed hinge-area (fig. 320), and a wide deltidium, 



Fig. 319. Trimerella 

 acntminata cast. Upper 

 Silurian. (After David- 

 son and King.) 



Fig. 320. Trimerella 

 grandis cast. Upper Si- 

 lurian. (After Davidson 

 and King.) 



Fig. 321. Monomerella 

 prisca cast. Upper Si- 

 lurian. (After Davidson 

 and King.) 



bounded by two ridges, the inner ends of which serve as 

 teeth, though true teeth are not present. Each valve is 

 furnished with muscular platforms, which, in the typical 

 species, are elevated and doubly vaulted. The principal, or 

 only, genera of the family are Trimerella, Dinobolus, and 



