105 



September 9, 1834. 

 Joseph Cox Cox, Esq., in the Chair. 



A letter was read, addressed to the Secretary 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- 

 hranchiated Gasteropodous Mollusca. The latter was accompanied 

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

 signation of 



Leptoconchus. 



Testa tenuis, pellucida, subglobosa, spira depressa, subobsoletel : 

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

 ginibus hand coalitis, dextro tenui antice subexpanso : columelld 

 nulla, umhilico nuUo, antice truncata, contorta. 



Animal proboscide elongato, retractili : tentaculis duobus, com- 

 planatis, trigonis, intern^ ad basin coalitis, externe in medio oculos 

 gerentibus : pede mediocri, operculo nuUo : palUo ad marginem cir- 

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

 mine branchiali submagno. 



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

 genus is constantly a sHghtly sordid milk-white. It is sulcated ex- 

 ternally 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, 14^ lines; greatest breadth, 12-J-; 

 length of the young shell, 74-; breadth, 6. 



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

 stantly occur imbedded in the calcareous mass of polypes, having a 

 communication with the sea by only a moderate opening. They 

 are found in the Red Sea, and are most frequently met with in 

 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 always 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. Ruppell suggests that the systematic place which should be 

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

 tentacula, the oral 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 which may 

 be added some of the characters of the shell : but he states himself 

 to be perfectly aware that the difference between the habitations of 



No. XXI. Proceedings of the Zoological Society. 



