MAZATLAN UNIVALVES 319 



365. CAECUM HEPTAGONUM, n. S. 



C. (Elephantulum) t. septangulatd, angulis valde prominenti- 

 bus ; annulis rotundatis confertis cinctd, angulos longitudinales 

 supracurrentibus ; aperturd planatd, extus heptagonis formd, 

 intus circulari, sulco concentrico ornatd ; operculo ? 



Although only a fragment was found, containing a perfect 

 mouth, the shell is so different from all other known species 

 of the genus, that it was thought best to name it and thus 

 direct attention to its existence. By its strong longitudinal 

 angles, it would rank with Elephantulum ; by its concentric 

 rings, (traversing these angles) with Anellum. The front view 

 of the aperture exactly resembles an old-fashioned clock-face 

 in miniature. In a flat surface with a heptagonal border is 

 eut a circular hole surrounded by a ring. The discovery of 

 this curious link, which was on the point of being discarded, 

 shews the importance of not rejecting fragments. The diame- 

 ter of the mouth is ext. "02, int. "015. 

 Hob. Mazatlan ; 1 imperfect sp. off Spondylus ; L'pool Col. 



Tablet 1524 contains the fragment. 



SECTION B. ANELLUM. 



C. t. rare elongatd,juxta aperturam parum constrictd, annulis 

 concentricis testa adultd cinctd. 



366. C^ICUM ELONGATUM, n. s. 



C. (Anellum) t. elongatd, tereti ; primum lavi, dein annulis 

 rotundatis, parum extantibus instructd, interstitiis minimis ; 

 septo ungulato, apice parum elevato, subobtuso, margine laterali 

 subrecto ; operculo ? 



? Var. SEMILJEVE ; t. hue et illuc annulatd, Jiuc et illuc Icevi. 



Known from C. firmatum by the elongated form, and by the 

 scarcely raised rounded rings with very small interstices ; also 

 by the plug, which is ungulate, with the apex not dextral and 

 rather broad. Of the ? variety, three specimens were found, 

 not perfect enough for description, but most probably distinct. 

 They seem to have relations with C. liratocinctum, but shew 

 no trace of longitudinal ribs. One fragment presents a few well 

 marked rings between smooth spaces. Another very large 

 but rubbed specimen has a sudden contraction followed by a 



