178 NORTH AMERICAN INDEX FOSSILS. 



f. Platforms very prominent with conical cavities beneath 55. 



55. Conical cavities very long, extending from one third to one half 

 the length of the shell as shown by the internal molds. 



V. Trimerella. 



55. Conical cavities short, extending about one tenth the length of 



the shell III. Dinobolus. 



f. Platforms not very prominent, solid (i. <?. , with no cavities beneath 



them) IV. Monomorella. 



3. Shell linguloid — Elongate, corneous, thin (except Lingulasma) g. 



g. Inequivalved (pedicle valve the larger, projecting posteriorly), spatu- 



late 66. 



66. Cardinal area distinct dd. 



dd. Shell minute (about ^ inch long).* VIII. Leptobolus. 

 dd. Shell larger (% to 3^ inch long) with high cardinal area. 



VI. Lingulella. 

 66. Cardinal area not distinct ; pedicle valve often much produced 



at beak VII. Lingulepis. 



g. Equivalved. Surface glistening 77. 



77. Platform present in the posterior portion of each valve. 



X. Lingulasma. 



77. No platform present • IX. Lingula. 



3. Shell pentameroid — Usually longer than wide and expanding in width 

 from beak to front. Beak generally incurved, not truncated by fora- 

 men, rarely with area. Sinus and fold variable. A spondylium in 



pedicle valve h. 



h. No radiating striae or plications 88. 



88. Sinus or fold present ee. 



ee. Small (average length I inch) LXII. Camarella. 



ee. Not so small f. 



f Umbo of pedicle valve very prominent and overarching *. 



* Sinus in pedicle valve and fold in brachial. 



LXVIII. Clorinda. 



* Sinus, when present, in brachial valve and fold in 



pedicle LXX. Gypidula. 



f Umbo of pedicle valve small LXVII. Pentamerus. 



88. Sinus or fold absent ff. 



ff. Umbo of pedicle valve prominent LXX. Gypidula. 



ff. Umbo small LXVII. Pentamerus. 



h. With radiating striae or plications, without area 99. 



99. Sinus or fold present gg. 



g%. Striae or plications absent from umbo ff. 



|f Small (average length ^ inch) LXII. Camarella. 



ff Large **. 



** Umbo of pedicle valve large LXX. Gypidula. 



** Umbo comparatively small i // . 



i // Shell outline subcircular. 



LXIII. Parastrophia. 

 l // Shell outline subtriangular. 



LXX II. Camarophoria. 



* All measurements refer to adults. 



