320 MAZATLAN UNIVALVES 



very large swelling previous to the aperture. It measures 

 long. '112, lab. (juxta aperturam) '025 '028. 



Of the typical form about a dozen sp. were found, but most 

 of them were rubbed. They present however the different stages 

 of growth. The youngest measures long. '06, lat. '008 "017. 



The largest '103 '015 '023. 



A fragment (? conspecific) '027. 



Hob. Mazatlan ; extremely rare, off Spondylus ; L'pool Col. 



Tablet 1525 contains 4 sp. and fragment of different ages, 

 typical form. 



Tablet 1526 contains 2 sp. ?var. semilaeve. 



367. CJECTJM STJBIMPBESSUM, n. s. 



C. (Anelltim) t. elongatd, kaud parva, solidiore ; annulis 

 creberrimis, rotundatis, liaud extantibus, interstitiis parvis, 

 scepius subimpressis ; septo mucronato ; margine later all mx 

 concavo ; mucrone parvd, obtusd, ad dors-urn sitd ; operculo 

 ? concavo. 



Of this species only 2 adult and 6 young specimens were 

 found ; these, being in different stages, have to be retained. 

 The sculpture and habit of growth resemble those of C. elonga- 

 tum ; from which it differs especially in the narrow mucro. 

 The only specimen possessing the operculurn is of aberrant 

 growth. The sutures are least impressed in the very earliest 

 stages. The smallest sp. measures long. '058, lat. '008 '016 



The largest '115, '017 '03. 



Hob. Mazatlan ; extremely rare, off Spondylus ; L'pool CoL 



Tablet 1527 contains 7 specimens in different stages of growth, 

 of which one possesses the operculum, and another is curiously 

 deformed. 



368. CJECUM FIBMATTJM, C. J5. Ad. (diagn. auct.J 



C. (Anellum) t. robustd, arcuatd, satis tereti ; aperturd vix 

 constrictd ; t. juniore primum l&vi ; dein annulis circiter 

 xxiii. xxxiii., primum acutioribus, dein parum qiiadratis ; 

 interstitiis subquadratis, plus minusve distantibus, interdum 

 aperturam versus evanidis ; septo subungulato ; apice parum 

 prominente, subdextrorsum sito, obtusiore, latiore ; margine ad 

 latus subrecto ; operculo ? . . . . 



