258 THE MARQUIS DE TOLIN ON TUB CiECIDTE. 



of this kind aifords the best possible proof that the septum is not 

 susceptible of translation. AVe have carefully preserved the 

 double CcBcum in two portions, together with specimens of 

 another species from the same locality, and which also exhibit 

 the adolescent and adult shells still united. 



Subjoined are the diagnoses of the two species in question : — 

 In conclusion, we find the septum invariably formed in the 

 interior, and thus preserved from any chance of irregularity. 

 But it should also be remarked that a structure of this kind, 

 in its destination, is not necessarily subject to laws originating 

 in immutable and inflexible forms under necessities of capacity, 

 and that under similar conditions the septum, without entirely 

 losing its character, may differ in size (faille), and undergo 

 slight alterations of form in different specimens of the same 

 species. 



CiECUM FORMULOSUM. (Plate VIII. fig. 4.) 



Testa parum conica, satis arcuata, aurantiaca, interdum alba, zonulata, 

 nitida, longitudinaliter costis validis rotundis et strigis satis regula- 

 ribus omata, transversim annidis crebris, planatis, paulo rotundatis, 

 primum angustis, dein crescentibus, postea majoribus decussata, 

 apei'turam versus baud tutnida ; apertura vix declivi, baud contracta, 

 nee marginata ; septo primum lajvigate raamillato ; apice submu- 

 cronato; margine laterali subrecto, paulo coueavo, interdum primum 

 convexo dein concave ; operculo . . . . ? 



Long. 00028, diara. 00005-00007. 



Hab. New Providence, Bahama. 



CiECUM DECUSSATUM. (PI. VIII. fig. 5.) 



Testa vix conica, satis arcuata, solida, aurantiaca sen albida, crystallina, 

 interdum subopaca, nitida, costis validis, rotundatis, et strigis minutis 

 longitudinaliter omata, transversim irregulariter striata, ad basim 

 tumida, tumore rotundato, aperturam versus annulis validis rotundis 

 decussata ; apertura paulo declivi, parum contracta, levitcr marginata ; 

 septo minimo, submucronato ; apice subdextrorso ; operculo . . . . ? 



0022, ,. J 0-0006. 

 •003, •*"™-l 0-0007. 

 Hab, New Providence, Bflhama. 



Long. I ^: 



RemarJcs on tlie genera Brochina and Strebloceras or Phleboceras. 



The authority of the learned author who created the genus 

 Brochina is so high that it is with hesitation that I venture to 

 express some doubt as to its existence. As tlio convexity of 



