TUE MABQUIS DE FOLIN ON THE OiBCIDJ3. 263 



tura declivi, hand marginata ; septo parvo, ungulato ; npice dextro ; 

 margine lateral! primum convexo, dein concavo, dorsali concavo j 

 operculo . . . ? 

 Long. 0-0015 m. ; diam. 0-0006 m. 

 Hab. Vera Cruz. 



The points of contact between the last of these species and a 

 well-marked Qcecum will be readily seen. I will take one which 

 is perhaps not the nearest approach to Q. veracruzmium, but which 

 at any rate resembles it very closely, and which has the most 

 perfect claim to be placed under the genus Ccecum ; this is C. cur- 

 • latum ; and we shall at once have established the relation which 

 unites the solitary species of BrocMna to the genus GoBcwm. It 

 consequently appears to me quite evident that no distinctive 

 character remains of the genus Brochina beyond the convexity of 

 the operculum ; and if we recall what has been stated above with 

 respect to shells not smooth being furnished with a convex oper- 

 culum (I refer to those prematurely named by us B. Someri and 

 B. achirona), it must be allowed that there is nothing to induce 

 us to regard the genus as sufficiently established. 



But my doubts have not been confined to the above genus alone; 

 I have also suspicions respecting Strehloceras or JPhleboceras. 

 Several specimens of primary shells having been met with in the 

 sands, they were subjected to a scrupulous examination. I 

 speedily noticed amongst them some specimens in which part of 

 the adolescent shell was already existing, upon which was plainly 

 evident the annular ornamentation of certain species ; it was 

 evident that these specimens could only belong to the genus 

 Ccscum. Close comparison of these young Csecums, and of other 

 shells belonging to the first stage, afibrded nothing which marked 

 any want of resemblance ; and consequently in my eyes all be- 

 longed to CeEcum. This observation gave rise to my doubts. 



However, having received from M. Deshayes specimens of his 

 fossil species S. Edwardsii, we noticed that the individuals of this 

 species presented the appearance of a shell belonging to the 

 CaecidfB, in which the three stages continued united, with a slight 

 deviation in the general plane. There was no contortion, as in 

 Mieioceras, but a slight inclination of the plane of the primary 

 stage relatively to that of the second ; and the second bore the 

 same relation to the third. From this I conceived that I was 

 justified in regarding the deviation as characteristic of the genus, 

 and that this particular was apparent only in the complete shells, 



18* 



