MOLLUSC A— GASTROPODA. 587 



f. Without interior platform CV1I. Capulus. 



aa. Apex pointed ft* 



ff. Apex straight LXXVII. Igoceras. 



ff. Apex curved but not enrolled. 



LXXVI. Orthonychia. 



11. Surface striate or faintly plicate, rarely smooth bb. 



bb. Beak not incurved fff. 



fff. Beak subcentral, muscle scars forming a circle at 



about mid-height VII. Scenella. 



fff. Beak excentric, striae fine or absent, muscle scars 

 horseshoe-shaped, open in front. 



VIII. Lepetopsis. 



bb. Beaks strongly incurved CVII. Capulus. 



**. Surface smooth or with few coarse and faint plicae e. 



e. Horseshoe-shaped muscle scar open in front 22. 



22. Beak scarcely incurved VIII. Lepetopsis. 



22. Beak strongly incurved but scarcely enrolled, surface often 



striate ...CVII. Capulus. 



e. Horseshoe-shaped scar open behind CCVII. Anisomyon. 



e. Muscle scar faint or absent, dorsum often carinate. 



LXXV. Palceocapulus. 



2. Aperture circular or oval, form unsymmetrical ***. 



***. Low, patelliform, surface often with oblique angulation and posterior 



truncation CCVI. Hercynella. 



***. High, curved, surface smooth or coarsely plicate. 



LXXVI. Orthonychia. 



2. Aperture partly closed 4*. 



4*. Closure by a thin platform, beak marginal, curved laterally. 



CIX. Crepidula. 

 4*. Closure by the thick, flattened lower portion of the body whorl. 



XCVI1. Velatella. 



Shell nautiliform, coiled in a single plane throughout, or apparently so II. 



II. All whorls in same plane, with median notch or reentrant in outer lip 



(Bellerophontid) 4. 



4. Shell with rounded dorsum, often modified by elevated or sunken fold 



bearing the slit-band 5*. 



5*. With large open umbilicus * f- 



f. Aperture abruptly expanding, trumpet-like, volutions scarcely em- 



bracing 11. 



33. With a long narrow dorsal slit, closed at aperture. 



XV. Salpingostoma. 

 33. With slit replaced by a series of elongate openings. 



XVI. Trematonotus. 

 f. Aperture not expanded into trumpet mouth 44. 



44. Lip with sinus but no slit band cc* 



cc. Dorso-ventrally compressed whorls, sinus shallow and 



broad X. Owenella. 



cc. Rounded whorls, umbilicus mostly small, sinus deep. 



XI. Protowarthia. 



44. Lip with well-marked slit and slit-band dd. 



dd. Surface with oblique revolving lines... XIV. Bucania. 



