BRACHI0P0DA—0RTHID2E. 

 LIV. Bilobites Linnaeus. 



259 



Small, strongly bilobed. Hinge line short. Teeth and sockets 

 obscure. Cardinal process small and simple. Shell substance 

 punctate. Siluric-Carbonic. 



186. B. bilobus (Linnaeus). Siluric. 



Cardinal extremities auriculate. Pedicle valve very convex ■ 



brachial valve varying from slightly concave to slightly convex. 



Fig. 309. Platystrophia lynx. Inter- FlG. 310. Bilobites varicus. Exterior 



ior of pedicle valve X l - A, delthyrium ; dorsal view X f an d interior of brachial 



o, ovarian impression ; /, pedicle muscle valve much enlarged ; J, cardinal process ; 



scar; r, diductor muscle impression; /, c, crura ; a, adductor scars. (After Hall.) 

 teeth ; v, vascular markings. (After Hall.) 



Differs from B. varicus in its smaller size, its more extended hinge 

 line, greater inequality of the two valves and in its few radial striae. 

 Niagaran of New York, Indiana, Wisconsin. 



187. B. varicus Conrad. (Fig. 310.) Devonic. 



Ventricose. Cardinal area of pedicle valve the higher. Fora- 

 men high and narrow. Surface unequally striated, only a few of 

 the striae being visible to the naked eye. Differs from B. bilobus 

 in its larger size, greater gibbosity, and proportionally shorter 

 hinge line. 



Helderbergian of New York, Tennessee, New Brunswick. 



LV. Dalmanella Hall and Clarke. 



Plano-convex or subequally biconvex, subcircular in outline. 

 Pedicle valve elevated and arched over the cardinal area. Surface 

 covered with fine, rounded, bifurcating striae which curve very con- 



