376 AKERA. 



covered with a thin, scarcely shining callus, which continues to 

 the vertex. Alt. 11, diam. 9 mill. (S.). 



Habitat unknown. 



H. serica E. A. Smith, Ann. Mag. N. H. (4), ix, p. 349, 1872. 



This is a remarkably roundly ovate species, very finely trans- 

 versely striated, which produces a somewhat silky appearance, and 

 having the region of the umbilicus covered by a very thin dull cal- 

 losity, which is extended along the whorl to the vertex. Although 

 the sculpture is very like that of the H. insculpta Totten, the form 

 is very different (S.). 



Genus AKERA Miiller, 1776. 



Akera Mull., Zool. Danicre, Prodr. seu Anim. Dan. et Norv., 

 etc., p. 242, type A. bullata. — A. Ad., Thes. Conch., ii, p. 572. — 

 Acera of many authors. — Aceras Locard. — Eucampe Leach, Syn. 

 Moll. Gt. Brit, p. 42. 



Shell ovate or oval-cylindric, thin, fragile, elastic, with exposed, 

 nearly level spire of several whorls. Last whorl acutely keeled at 

 the shoulder, the keel bounding a flat anal fasciole. Aperture nearly 

 as long as the shell, narrow above and extending in a deep sinus 

 along the sidtire, dilated below and very effuse, permitting all the 

 whorls to be seen from the base through the spirally ascending col- 

 umella. Columella very concave, thin, with narrowly reflexed 

 edge. Type A. bullata. 



Animal not completely retractile ; head disc depressed, long and 

 narrow, truncated in front, tapering behind ; eyes lateral, distinct. 

 Mantle rudimentary, enclosed in the shell, having a posterior fleshy 

 lobe passing backward and ascending the spire in the anal fasciole. 

 Foot long and narrow ; parapodial lobes very large, reflexed over 

 the shell, (pi. 48, fig. 5. A bullata). Stomach containing about a 

 dozen subtriangular, pointed, large and small cartilaginous plates. 



Jaws (pi. 61, fig. below f. 26, and fig. 29) separate, oval, reticu- 

 lated. 



Radula (pi. 61, figs. 30, 31, A. bullata) composed of many longi- 

 tudinal rows. Central tooth subtriangular with bilobed base and 

 reflexed, serrate cusp. Inner laterals falcate, with long serrate 

 cusps ; outwardly the cusps become longer and gradually lose the 

 serration, the outer teeth being acicular. 



