366 NORTH AMERICAN INDEX FOSSILS. 



33. Surface with concentric sculpture strongest XIX. Edmondia. 



I. Pallial sinus present ; also pallial line rather strongly impressed. The following 



characters also usually hold true : Resilifer present ; hinge line straight, 

 moderately long. Hinge and basal margins parallel. Umbos prominent.. 2. 



2. Most prominent surface sculpture concentric c. 



c. Concentric sculpture strongest medially CXX. Allorisma. 



c. Concentric sculpture strongest anteriorly 44. 



44. Surface sculpture all concentric CXXII. Rhylimya. 



44. Surface sculpture radial in middle of shell CXXIV. Pholadella. 



44. Surface sculpture radial posteriorly ff. 



ff. Umbonal ridge angular CXXV. Cimitaria. 



ff. No umbonal ridge present CXXVIII. Anatimya. 



c. Concentric sculpture uniform over entire shell 55. 



55. Middle of each valve with radii CXXIX. Liopistha. 



55. Middle of valves free from radii gg. 



gg. Hinge margin with a thin horizontal lamina.. CXIX. Pleuromya. 



gg. Hinge margin with no lamina 5f. 



5f. An anterior sinus present, extending from beak to base. ..5*. 



5*. Teeth present CXXI. Sphenotus. 



5*. Teeth absent CXXIII. Endodesma. 



5f. No sinus on anterior portion of shell XVIII. Chcenomya. 



2. Most prominent surface sculpture radial, strongest medially, wanting pos- 



teriorly d. 



d. Posterior umbonal ridge well marked dorsally CXXIV. Pholadella. 



d. Posterior umbonal slope gently rounded 66. 



66. Shell attenuate posteriorly CXXVII. Phenacomya. 



66. Shell broadly rounded posteriorly hh. 



hh. Beaks subcentral CXXIX. Liopistha. 



hh. Beaks anterior CXXVI. Pholadomya. 



B. Distinct hinge plate present II. 



II. Shell winged or eared, i. e., the flattened dorsal portion is extended beyond the 



convex body of the shell and more or less definitely constricted from it. 

 Hinge line straight 3. 



3. Hinge line marked with numerous vertical grooves for reception of ligament... £. 



e. Beaks terminal 77- 



77. Concentric sculpture prominent LXVII. Inoceramus. 



77. Concentric sculpture not prominent ii. 



ii. Posterior portion of hinge without teeth LXVI. Gervilliopsis. 



ii. Posterior portion of hinge with teeth 6f. 



6|. Anterior and posterior lateral teeth parallel to hinge margin. 



LXIV. Bakewellia. 

 6f. Anterior and posterior lateral teeth ranging obliquely upward. 



LXV. Gervillia. 



e. Beaks not terminal 88. 



88. Surface with prominent radiating sculpture XCVI. Crenipecten. 



88. Surface with prominent concentric sculpture... LXVI I. Inoceramus. 

 88. Body of shell with concentric and ears with radial sculpture ; beak 



subcentral XCIII. Euchondria. 



3. Hinge line not marked with numerous vertical grooves for the ligament..... f. 



f. Shell ostreiform, i. <?., strongly inequivalve, distorted by early adherence 



to other objects. Only one muscle scar present, subcentral. Teeth 



