127 



luto, plus minusve tuntentei wu&gine luieraU eoneexo, dorsum 



versus suhangulata i operculum .' — . 

 Long. -11, lat. •018--024. 

 I lab. Sutton, Cor. Crag. Bins. Brit. &C. 



= C. trachea, Scnrlcs Wood, Crag. Moll. ]». 115. pi. 20. f. 5 

 (? pars), non Mont, et auct. 



It is with great hesitation that I venture to differ from so accurate 

 an authority as the author of the 'Crag Molhisca : ' nevertheless, 

 having subjected all the specimens in the British Museum, as well 

 as some sent me by Mr. Wood, to a very rigid examination under 

 the microscope, I have not been able to find a single specimen t hut 

 can be strictly affiliated to C. trachea. Of the minute sculpture 

 in a crag shell, little can be said ; the majority of specimen- are 

 almost smooth. The recent species is, however, peculiar in tbe cha- 

 racter of the aperture, never showing even an approach to the swell- 

 ing mouth of the fossil; and the plug of the latter is completely 

 mamillated, though with a flattening and incipient apes at the dorsal 

 Bide. When compared with the swollen variety of the recent shell, 

 the front of the latter displays an irregularity of outline which con- 

 trasts strongly with the beautifully rounded fossil, and proves it to 

 be of abnormal growth. The B.M. specimens being somewhat mixed 

 on the tablets, it is probable that the magnified plug in the figure 

 of this species is really an individual of C. mamillatum, with the 

 mucro rubbed off. 



18. Cecum firmatum, C. B. Ad. (diagn. auct.) 



C. (Anellum) t. robusta, satis tereti ; t.jun. p r i mum la-ri, dein 

 annulis circ. xxiii.-xxxiii., primum acutioribus, dein parum 

 quadratics interstitiis subquadratis, interdum evamdie; septo 

 subunyulato ; apice parum prominentc, subdextrorsum sito, ob- 

 tusiore; maryine laterali subrecto : operculo vix couccvu, su- 

 turis minus definitis. 



Test. jun. long. -06/, lat. '006— -012. 



Test. adol. long. '0G3, lat. -013— -017. 



Test, adult. -1, lat. 016— -025. 



llnh. Panama, common (C. B. Adams) ; Mazatlan, rare, oft' Spon- 

 dvhu and among Olivellce. Mus. Brit. 



Pars= C'cecum Jirmatum, C. B. Ad. Pan. Shells, no. 213, pp. 161, 

 311. 



+ 0. ebumeum, C. B. Ad. no. 212. pp. Kil, .".1 1. 



+ (adolesc.) C. munstrusum, C. B. Ad. no. 2 Id. pp. 162, .il 1. 



+ (adolesc.) ('. pyonueum, ('. B. Ad. no. 218. pp. 163, 31 1. 



-1- (jun.) O. dinuxutum, C. B. Ad. no. 21 I. pp. 161, SiO. 



Bias. Cat. p. 320. 



Known from C. trachea by the itOUt sidxpiadiat. rings. It the 

 mode of specific diagnosis adopted by Prof Adam- had been fol- 

 lowed in this monograph, the number "f species (wherever il>. 

 cimens were sufficiently abundant) would have had to be mere 

 fivefold. 



