105 



September 9, 1834. 

 Joseph Cox Cox, Esq., in the Chair. 



A letter was read, addressed to the Secretarj' by Dr. E. Riippell, 

 and dated Frankfort, August 10, 1834. It was accompanied by 

 specimens of Magilus antiquus, Rupp., including both the shell and 

 the animal, and of the shell and animal of a new genus of Pectini- 

 branchiated Gasteropodous MoUusca. The latter was accompanied 

 by a description by Dr. Riippell, who characterizes it under the de- 

 signation of 



Leptoconchus. 



Testą tenuis, pellucida, subglobosa, spira depressa, subobsoletž, : 

 aperturd magna, subovali, extreniitatibus in contrarium versis, mar- 

 ginibus haud coalitis, dextro tenui anticė subexpanso : columelld 

 nullžl, umbilico nulio, anticė truncata, contorta. 



Animal proboscide elongato, retractili : tentaculis duobus, com- 

 planatis, trigonis, internė ad basin coalitis, extemė in medio oculos 

 gerentibus : pėde mediocri, operculo nulio : pallio ad marginėm cir- 

 culari, haud appendiculato, ad latus sinistrum subproducto : fora- 

 tnine branchiali submagno. 



The colour of the shell which constitutes the type of this new 

 genus is constantly a slightly sordid mLlk-white. It is sulcated ex- 

 temaUy by numerous longitudinal undulated closely set lines, the 

 outer whorls encroaching on the spire of the earlier ones so as almost 

 to obliterate it. 



Length of the adult shell, 144- lines; greatest breadth, 124-; 

 length of the young shell, 7-į- ; breadth, 6. 



Individuals of all ages have the shell thin and fragile, and con- 

 stantly occur imbedded in the calcareous mass of polypes, ha\'ing a 

 communication with the sea by only a moderate opening. They 

 are found in the Red Sea, and are most freąuently met with iu 

 Meandrina Phrygia. 



To distinguish the shell of Leptoconchus from that of Magilus it is 

 sufficient to observe that in the latter the two margins of the aper- 

 ture are alvvays united, while in the former genus they are always 

 disunited. The animals are distinguished by the possession and 

 the want of an operculum, and by the difference in the proboscis ; 

 the siphon of Magilus, moreover, does not occur in Leptoconchus. 



Dr. Riippell suggests that the systematic place which should be 

 assigned to this genus is near the lanthina. The number of the 

 tentacula, the orai proboscis, the mantle destitute of siphon, the pec- 

 tinated branchice composed of closely heaped pyramids, and the ab- 

 sence of operculum, are so many marks of affinity ; to ■vvhich may 

 be added some of the characters of the sheU : but he statės himself 

 to be perfectly aware that the difference between the habitations of 



No. XXI. Proceedings of the Zoological Society. 



