THE MOLLUSCS OF THE GREAT AFRICAN LAKES. 199 



vations on this point. Lastly, T have found the style and its 

 sac to be present in Ty phobia, where it has exactly the same 

 relations to a stomachic caecum as in S trombus, Pterocera, 

 or in those Lamellibranchiata in which this structure is 

 present. I may also remark that the crystalline style and its 

 caecum are present in the so-called Lithoglyphus of Tan- 

 ganyika, the affinities of which Gastropod have been entirely 

 misinterpreted. 



From the complete similarity of the style, and more especi- 

 ally of the stomachic csecum, in those Lamellibranchiata which 

 possess it, and in those Gastropods where it is also present, 

 there can be little doubt, as Collier, Huxley, and Woodward 

 have already clearly seen, that the structures are in reality 

 strictly homologous throughout. But the great importance 

 and suggestive character of this conclusion has been much 

 obscured by Fischer^ and others who confuse the true crystalline 

 style in its sac with the doubtful structure known as the 

 " Fleche tricuspide." There is little doubt that the"Fleche" 

 has in the majority, if not in all cases been merely the cuti- 

 cular lining of the stomach which has become detached, as it 

 most readily does. With the appearance thus produced are to 

 be classed the bodies described by Fischer in the stomachs of 

 Cyclostoma and Paludina. Young^ also describes in 

 Helix pomatia a cuticular lining to the intestine, which he 

 erroneously compares with the crystalline style of the Lamelli- 

 branchs. There appears to be no similarity between the CEecum 

 described by Cuvier and Keferstein^ in Buecinum and that 

 in Strombus and the Typhobias. Further investigation 

 is, however, undoubtedly required.* 



^ ' Manuel d. Conchyliologie,' p. 41. 



* ' Mem. Cour. Acad. Belg.,' 4to, t. xlix, No. 1, p. 34. 



2 Bronn's ' Klassen u. Ordnuug. d. Thier-Reichs/ Bd. iii, Abtli. 2, Mala- 

 cozoa, 1862-66. 



* Apart from their bearing on the aflBnities of the Typhobias, the above 

 observations show that the generally taught hypothesis vphich originated vrith 

 Meckel and Garner, and depicts the caecum in the Lamellibranchiata as 

 homologous vpith the radular sac of the Gastropods, and the style of the former 

 with some part of the ddontophore of the latter, must be utterly unsound. 



