GASTEROPODA. 117 



3. Caecum glabrum. Mont. Tab. XX, fig. 6. 



Dentalium glabrum. Mont. Test. Brit. p. 497, 1803. 

 CiECUM glabrum. Flem. Edin. Ency. vii, p. 67, t. 204, fig. 7, 1817. 

 Orthocera Glabra. Flem. Brit. An. p. 237, 1828. 

 Dentalium glabrum. Turt. Conch. Diet. p. 40, 1819. 

 Brochus glabkus. Brown. Illust. Brit. Conch, pi. 1, fig. 3, 1827. 



— l^vis ... pi. 1, fig. 6. 



Ca:cum glabrum. S. Wood. Catalogue 1842. 

 Dentalium glabrum. Thorpe. Brit. Mar. Conch, p. 4, fig. 5, 1844. 

 Dentaliopsis glabra. Clark. MS. 1847. 



C. Testa pusilld, cylindricd, arcuatd, laevigata poliid; antice simplici, non margi- 

 natd ; postice clausd, obtusd, convexd, submarginatd. 



Shell very small, cylindrical, curved, smooth, and glossy ; anterior extremity 

 simple, not marginated or thickened ; posterior termination, with an obtuse convex 

 clausum, submarginated. 



Length, yg- of an inch. 



Locality. Cor. Crag, Sutton. Recent, Britain. 



I have only two specimens of this shell ; they, however, are so precisely similar 

 to the recent species, that I have no hesitation in considering them identical. 

 They are perfectly smooth, smaller than any of my specimens of C. mammillatum, 

 and they are more particularly distinguished by having the posterior termination 

 closed by a perfectly convex clausum, marginated by the edge of the shell. 



4. CiECUM (?) incurvatum (?) . Walker. Tab. XX, Fig. 7, a — b. 



Serpula incurvata. Walker. Test. Min. Rar. fig. 11, 1787. 

 Vermiculum incurvatum. Mont. Test. Brit. p. 518, 1803. 

 Serpula incurvata. Turt. Conch. Diet. p. 156, 1819. 

 Cornuoides major. Brown. Illust. Brit. Conch, pi. 1, fig. 49, 1827. 

 Serpula (?) recta. S. Wood. Catalogue 1842. 



C. Testa minima, laevigata, politd tenia, fragili ; antice cylindraced, apertd, non mar- 

 ginatd ; postice incurvd, convolutd. 



Shell very minute, smooth, glossy, thin, and fragile ; anterior portion cylin- 

 drical, with a simple but not marginated aperture ; posterior portion incurved, 

 with two volutions. 



Length, nearly \ a line. 



Locality. Cor. Crag, Sutton. ? Recent, Britain. 



Three specimens of this minute shell, found by myself in the sand of the 

 Coralline Crag, appear to resemble the figures given of the recent species. 



Mr. Jeffreys informs me that he believes this to be only the young or immature 

 state of Cacum glabrum, and that decollation takes place at a certain period of its 

 existence when the posterior termination is differently closed. Until further 

 observations shall have confirmed the correctness of this opinion, it may be as well 

 to allow it to remain as a distinct species, in proximity with what are, no doubt, 

 its true relations. 



