150 MOLLUSC A FROM THE CRAG. 



margin obtusely angulated ; spirally striated, with fine undulating striae ; rough and 

 imbricated beneath, aperture expanded ; umbilicus wide and open. 



Greatest diameter, 1 line. 



Locality. Cor. Crag, Sutton. 



I have only two small specimens of this delicate and tender shell, which may 

 possibly be the young of some larger species ; it somewhat resembles Sig. Leachii 

 (Sowerby's Gen., fig. 3), Cryptostoma Leachii, Blain., but it appears to difi^er in several 

 particulars : the outer margin of the volution is more angulated, forming a flattish base, 

 which is rough and strongly imbricated by reflected lines of growth, and the umbilicus 

 is large, open, and visible up to the apex. 



Marsenia, Leach, 1820. 

 Bulla (spec.) Mont. 

 Lamellakia (spec.) Mont. 

 CoRiocELLA. Be Blainville, 1824. 

 Chelinotds. Swains. 1840. 

 SiGAKETCS Flem. Phil. Thorpe. 



Gen. Char. Shell internal, convolute, ear-shaped, thin, delicate, fragile, pellucid, 

 semipapyraceous ; consisting of a few rapidly increasing volutions, and an expanded 

 aperture, with a small depressed spire ; peritreme sharp and thin, confluent with the 

 columella, which is visible internally up to the spire ; shell wholly enveloped by the 

 mantle of the animal. 



In my Catalogue the above generic term was employed, in consequence of Dr. 

 Leach having given that name to the well-known British species, BuUa haliotoidea, 

 Mont., in his ' Mollusca,' a part of which was printed in 1820. A species of this 

 genus was described also by Montague (in the Linn. Trans., 1815, vol. ii, p. 186), 

 under the name of Lamellaria, and included with an animal of quite a difi'erent form, 

 which he had considered as its type, from which therefore it must be removed. In 1825 

 M. de Blainville (in his System of Malacology) proposed a genus under the name of 

 Coriocella ; but in his description of C. nigra, from the Isle of France, the animal he 

 considered as the type of his genus, he states that no trace whatever of a shell could 

 be discovered, "sans trace de coquille ext6rieur niinterieur" (p. 466). "Specimens of 

 Coriocella nigra in the British Museum, presented by Cuvicr, and described by 

 De Blainville, have a distinct shell." (Vide Gray, Zool. Proc, 1847, p. 143.) 



As the name Marsenia was given to a determined species, and published with the 

 ulterior intention of characterizing such genus, it is I conceive the one that ought 

 to be adopted. 



