MANUAL OF TEE MOLLUSCA. 



Ophlleta, Yanuxem (p. 267), was founded on species of 

 Madurea, -with very slender whorls. Mr. Billings regards tliem 

 as distinct, and distinguishes them as follows : — ' ' In Madurea 

 the aperture is entire, and the whorls usually large, but in 

 Ophileta it has a sinus below and a notch above, while the 

 whorls are usually more slender. 



"In Madurea crenuJata (Billings) there is a sort of spiral band, 

 and also there are indications of a sinus in the lip on the flat 

 side, but they are only incipiently developed." — (Billings.) 



STfiOPHOSTYLTJS, Hall. 



Etymology, strejpho, I tui'n, and stylus, columella. 



Shell subglobose or ovoid ; spire small, body whorl large and 

 ventricose ; outer lip thin ; columella twisted or spirally grooved 

 within, not reflected ; umbilicus wanting ; aperture ovate or 

 transversely oval ; apparently related to Flaty stoma. 



Distribution, 10 species. Silurian. United States. 



Helioceypttjs, D'Orbigny, 1850. 



Shell depressed, orbicular ; whorls embracing ; umbilicated 

 on both sides ; aperture vertical, oval transverse. 



Distribution. H. pusillus. Coral Eag, France, Germany ; 

 H. radiatus, TJ. Gr. S. Blackdown, Mans. 



[Family LANTHiNiD-a;] 

 Includes — 

 Llnthtna and EECLrzLi (see p. 285). 



Family XII.— Calypte^idje.* 

 Platyceras, Conrad, 1840 (see p. 277). 



Type, Pileopsis vetusta, Sowerby. 



Synonyms, Acroculia, Phillips, 1841; Orthonychia, Hall, 1843. 



Shell depressed, subglobose to oblique, subcorneal; spii'e 

 small ; whorls few, free or contiguous ; aperture more or lesa 

 expanded, often campanulated, entire or sinuous. 



Many species show a sinuosity of the striae, indicating a notch 

 in the margin of the aperture during the first stages of growth. 

 Mr. Hall has been unable to recognise the peculiar muscular 

 impressions which are characteristic of Pileopsis. Specimens o^ 

 gome species show the expansion of the columellar lip, and its» 

 partial or entire union with the volution, presenting all the 



* See p. 275. 



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