MAZATLAN TTXIVALVE8 319 



365. C^CXTM HEPTAGONUM, n. S. 



C. (Elephantulum) i. septangulatd, angulis valde 2}>'ominenti- 

 hus ; anmiUs rotundatis confertis cinctd, angulos longitudinales 

 swpracurrentihus ; aperturd planatd, extus heptagonis forma, 

 intus circiilari, sulco concentrico ornatd ; operculo ? . . . . 



Altliough only a fragmeut 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 AneUum. 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 siu-rounded by a ring. The discovery of 

 tliis 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. 



Hah. — Mazatlan ; 1 imperfect sp. oflF Spondylus ; I! pool Col. 



Tablet 1524 contains the fragment. 



Section B. Axelltjm. 



C. t. rare elongatd,juxta aperturatn parum constricta, annulis 

 concentricis testd adultd cinctd. 



366. CiECUM ELONGATtJM, n. S. 



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

 rotundatis, parum extantihus instructd, interstitiis minimis ; 

 septo ungulato, apice parum elevato, subobtuso, margine laterali 

 suhrecto ; operculo ? . . . . 



? Var. semil;eve ; t. hue et illuc annulatd, hue et illuc IcBvi. 



"Known from C. fii'matum by the elongated form, and by the 

 scarcely raised rounded rings with very small intei-stices ; 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. liratociuctum, 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 



