432 



contract a ; annulis rotundatis paucis, subobsoletis, aperturam 

 plerumque prcecedentibus ; septo submucronato ; apice subpro- 

 minente, haud acuto ; margine laterali subtumido : operculo 

 concavo, suturis distinctis, peripheriam versus linea elevata 

 instructis. 



Long. -064, lat. -019. 



Hob. Mazatlan, very rare in Spondylus ; and living among Oli- 

 vellcB. Mus. Brit. 



Maz. Cat. p. 326. 



This species differs from C. Iteve not only in the more slender 

 shape and submucronate plug, but also in the spiral rib round the 

 outer whorls of the operculum, which was found in four specimens. 



29. Cecum vitreum, Cpr. 



C. (Fartulum) t. subelongata, vitrea, nitida ; apertura parum 

 declivi, vix contracta et postea refiexa ; aperturam versus tu- 

 midiore ; septo prominent e, mucronato ; margine laterali recto 

 seu subconcavo ; mucrone plus minusve obtuso, subdextrorsum 

 sito : operculo 1 . . . 



Test. jun. long. -038, lat. -007— 'Oil. 



Test. adol. long. -073, lat. 01 — 018. 



Test, adult, long. -107, lat. -017— '023. 



Hab. Teneriffe, 50 fms. gravel (M' Andrew). Mus. Brit. &c. 



Ccecum glabrum, M'Andr. Geogr. Distr. Test. 1854; B.M. Cat. 

 Shells Canar. p. 29 (non Mont.). 



Ccecum vitreum, Cpr. in M'Andr. Rep. Moll. N.E. Atl., Br. Ass. 

 1856. 



More than 100 specimens were found of this species, which is 

 characterized by its somewhat tapering shape, and obtusely mucro- 

 nated plug. The surface sometimes displays annular lines of growth. 



29 b. Caecum (? vitreum, var.) Clarkii. 



C. (Fartulum) t. " C. vitreo " simili, sed minore, magis tereti ; 



septo ungulato ; apice obtusiore : operculo 1 . . . 

 Yariat margine laterali valde convexo, tumente. 

 Test. jun. long. -042, lat. -008— -013. 

 Test, adult, long. '082, lat. -013— -015. 



This is probably a "distinct species from C. vitreum ; but as the 

 plugs in each form are more variable than usual, the species is not 

 constituted till more is known. About fifty specimens were found. 

 It is named after the first discoverer of the animal in this interesting 

 genus. 



Hab. Teneriffe, 50 fms. gravel (M' Andrew). Mus. Brit. &c. 



30. CiECUM POLLICARE, n. S. 



C. (Fartulum) t. "C. vitreo" simili, sed plerumque magis tereti ; 

 nitida, sed striulis minimis tota superficie longitudinaliter cor- 



