GASTEROPODA. 13 



sented it as sufficiently elongated. Fig. 15 is the representation of a shorter and more 

 inflated variety, which might perhaps be considered as a species, with the name of 

 intermedins, except that C. myosotis has in itself a tendency to extraordinary variation, 

 and coming from a formation in which we are presented in other species with so 

 many monstrous forms, we may be allowed, if necessary, a more than common 

 deviation in this case. The number of teeth upon the columella being three, with a 

 slight difference in their size and inclination, at one time induced a belief that it might 

 be distinct, but the recent species, possessing even a greater degree of variation, will 

 justify this being considered only as a variety. One specimen from the cabinet of 

 Capt. Alexander, and one of my own, are all that I have seen from the Mammalif erous 

 Crag. 



Ord. PECTINIBRANCHIATA, Cuv. 



Sect. a. SOLENOSTOMATA, Flem. 



Gen. Ovula,* Bruguiere, 1792. 



Amphiceras. Gronov. 1/81 (fide Gray). 

 Ovulus. Be Montfort. 1810. 

 Simnia. Leach. 1819. Risso. 1826. 

 Ovulum. G. B. Sowerby. 18— (?) 

 Bulla (spec.) Linn. 

 Calpurna. Flem. 1828. 

 Birostra. Swains. 18 JO. 



Gen. Char. Shell fusiform or oviform, sometimes attenuated or greatly extended 

 at each extremity ; externally smooth or very finely striated ; convolute upon a 

 nearly horizontal axis, with a hidden spire ; aperture elongate and narrow ; outer 

 lip generally inflected and denticulated ; inner lip smooth. 



In form and mode of volution this genus approaches some of the species in the 

 genus Bulla, especially Bulla acuminata; but it may be distinguished from that 

 genus by its having both extremities of the aperture canaliculated. In this a fold 

 or tooth-like projection is visible at the upper part above the spire, whereas in 

 Bulla, the fold, when visible, is upon the columella. , The surface of the shell, when 

 it has attained its full size, is covered with an enamel-like coat, which is the exten- 

 sion of the columella lip ; and it is therefore supposed that the animal has a mantle 

 so extensive as to be able to envelope the entire shell. It differs from Cyprsea 

 principally in the ventricose smooth body of the volution, and in the absence of 

 denticulations on the columellar lip. 



In a recent state the greater number of known species are natives of a warm 

 climate, and one is quoted as an inhabitant of the British seas. It is not as yet 

 known below the tertiary formations, and two British fossil species have been 

 published, one of which is from the Crag. 



* Etym. The diminutive of ovum, an egg. 



