150 MOLLUSCA FROM THE CRAG. 



margin obtusely an gulated ; 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 differ 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. 



Maesenia, Leach, 1820. 



Bulla (spec.) Mont. 

 Lamellaria (spec.) Mont. 

 Coriocella. De Blainville. 1824. 

 Chelinotus. Swains. 1840. 

 Sigaretus 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, Bulla 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 different 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 exterieur ni interieur " (p. 466). 

 " Specimens of Coriocella nigra in the British Museum, presented by Cuvier, 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 characterising such genus, it is I conceive the one that 

 ought to be adopted. 



