312 MAZATLAN UNIVALVES 



This operc-olum within looks like a purple basin with a thin, 

 narrow, transparent rounded edge, and a stout boss rising up 

 in the middle. The outside, wliich was much incrusted, has 

 the layers rising sharply from the surface up the spire. The 

 concentric lirulse are distinctly marked within (except on the 

 boss) with a conspicuous termination, but the margin shews no 

 break. The colour near the boss is extremely deep. It is 

 clearly congeneric but not conspeeific with the last. 



Tablet 1513 contains the only specimen found. 



Family CyECID^. 



These creatures, ranked by Fleming among the Foraminifera, 

 by Philippi (a prima manu) among the Pteropods, and after- 

 wards, along with the Vermetidse between Eulima and Siph- 

 onaria, are arranged by Gray between Eissoa and jMelania. 

 Their natural allocation however appears to be between Ver- 

 metus and Turritella, as assigned by Forhes Sf Sanley (Br. 

 Moll. iii. 176) and by Clarh (Moll. Test. Mar. Brit. p. 322.) 

 They yet seem sufficiently distinct both in animal and shell, to 

 be separated, as a family, from each of their congeners. 



Gefus CiECUM, Flem. 



Ccecum, Flem. 1824, Edinh. Enci/cl. vol. vii. p. 67, et auct. 

 Brochus + PCornuoides, Browti, 1827, Conch. Gr. Br. pp. 124, 125. 

 Odontina, Zhorzewski, 1834, Mem. Soc. Mosc. iii. p. 310. 

 Odontidium, Phil. 1836, Emim. Moll. Sic. vol. i. p. 102. 

 Caecalium, Macgil. 1843, Moll. Aberd. 

 Cjecnm, Phil. Handb. Conch, p. 197 :— IT. Sf A. Ad. Gen. i. 



355 : — Clark, loc. cit. 

 Dentaliopsis, Clark, ms. 1834 

 Corniculina, Mun^ter. 

 Odontostoma, Cantr. non Phil. 



For a full account of the animals of the British species, 

 V. Clark loc. cit. to whose patient researches, long hidden 

 from the world, is due the first clearing of the mystery attend- 

 ing these curious little sliells. The animal of the N. England 

 species, C. pulehcllum, has also been described by Stimpson, 

 Proc. Bost. Soc. N. II. Oct. 1851. With regard to the shells, 

 errors have arisen from supposing that the adult form generall}- 

 seen immediately follows the spiral part known to be the early 

 stage of C. glabrum, and therefore believed to be characteristic 



