312 MAZATLAN UNIVALVES 
This operculum within looks like a purple basin with a thin, 
narrow, transparent rounded edge, and a stout boss rising up 
im the middle. The outside, which was much incrusted, has 
the layers rising sharply from the surface up the spire. The 
concentric lirule 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 conspecific with the last. 
Tablet 1513 contains the only specimen found. 7 
Famity CAICID. 
These creatures, ranked by Fleming among the Foraminifera, 
by Philippi (A prim& manu) among the Pteropods, and after- 
wards, along with the Vermetide between Eulima and Siph- 
onaria, are arranged by Gray between Rissoa and Melania. 
Their natural allocation however appears to be between Ver- 
metus and Turritella, as assigned by Forbes § Hanley (Br. 
Moll. 11.176) and by Clark (Moll. Test. Mar. Brit. p. 322.) 
They yet seem sufficiently distinct both im animal and shell, to 
be separated, as a family, from each of their congeners. 
Grerus CAICUM, lem. 
Cocum, Flem. 1824, Hdinb. Encycl. vol. vu. p. 67, et auct. 
Brochus + PCornuoides, Brown, 1827, Conch. Gr. Br. pp. 124, 128. 
Odontina, Zbhorzewski, 1834, Mem. Soe. Mose. iui. p. 310. 
Odontidium, Phil. 1836, Hnwm. Moll. Sic. vol. i. p. 102. 
Cecalium, M/acgil. 1843, Moll. Aberd. 
Cxcum, Phil. Handb. Conch. p. 197:—H. & A. Ad. Gen. 1. 
300 :— Clark. loc. cit. 
Dentahopsis, Clark, ms. 1834. 
Corniculina, Munster. 
Odontostoma, Canir. non Phil. 
For a full account of the animals of the British species, 
v. Clark loc. cit. to whose patient researches, ong hidden 
from the world, is due the first clearing of the mystery attend- 
ing these curious little shells. The animai of the N. England 
species, C. pulchellum, has also been described by Stévimpson, 
Proc. Bost. Soc. N. H. Oct. 1851. With regard to the shells, 
errors have arisen from supposing that the adult form generally 
seen immediately follows the spiral part known to be the early 
stage of C. giabrum, and therefore believed to be characteristic 
