1849.] SHARPE ON THE GENUS TYLOSTOMA. 377 



shells of this genus may be instantly recognised : in this respect they 

 bear some resemblance to several species of Ranella, with which 

 genus, however, there is no danger of confounding them, as they 

 have no canal nor notch to the aperture. 



M. D'Orbigny's genus Pterodonta, which belongs to a very dif- 

 ferent family of Gasteropods, presents some strong analogies to the 

 shells before us in having a longitudinal callosity within the outer lip. 



These shells are abundant in Portugal in all the calcareous beds of 

 the upper and middle parts of the cretaceous system, and form a 

 most useful guide to the geologist in that country. It is remarkable 

 that they should have been rarely noticed elsewhere. One species is 

 figured without a name in a curious old Spanish work on Organic 

 Remains, ' Apparato para la Historia Natural Espafiola,' by Joseph 

 Torrubia, Madrid 1754 ; I have in consequence named it after that 

 author. The only other allusion to these shells which I have met with 

 occurs in the ' Bulletin de la Societe Geologique de France,' of the 

 15th of May 1843, vol. xiv. pp. 505-512, where they form part of 

 the subject of a rather warm controversy between M. Charles Des- 

 moulins and M. Alcide D'Orbigny, which I am forced to touch 

 upon, as the subject would otherwise be left incomplete. 



M. Desmoulins objects to the genus Globiconcha, D'Orb., that it 

 is founded on imperfect specimens belonging in reality to Dolium, 

 and states that he possesses specimens of the G. Marrotia7ia, D'Orb., 

 some of which have a longitudinal constriction {enfoncement longitu- 

 dinal) bounding the outer lip, and proving the existence of an inter- 

 nal callosity, followed by an external enlargement of the lip. Other 

 specimens show that the callosity of the mouth is repeated at inter- 

 vals ; and others, that the columella is hollow ; while certain of his 

 specimens show that the G. 3Iarrotiana has not always the sunk 

 spire represented in the figure of the * Paleontologie Fran9aise,' 

 pi. 170. fig. 1, 2, but has sometimes an elevated spire like that of 

 G. rotundata, pi. 167. fig. 17 of the same work. 



There can be no doubt, that some, at least, of the specimens thus 

 referred to by M. Desmoulins belong to the genus Tylostoma ; and 

 if the whole of the specimens mentioned by him really belong to 

 Globiconcha Marrotiana, there can be no necessity for a new genus ; 

 but the characters of the genus Globiconcha must be modified so as 

 to admit the species described in this paper. It is, however, impos- 

 sible to suppose that so acute an observer as M. D'Orbigny, in de- 

 scribing the genus Globiconcha, should have assigned to it a '^ labre 

 mince, sans dents,'''' if it really possessed the more important charac- 

 ters which are found in the genus Tylostoma, and that his artist 

 should also have omitted them entirely in the figures. Such an 

 omission might occur with small shells of the size of the G. rotun- 

 data and G. Fleuriausa, 1. c. figs. 17 & 18, which might be too 

 young to show the callosity of the lip ; but in the larger specimens 

 figured of 6r. Marrotiana and G. ovula, pi. 170. figs. 1, 2 & 3, these 

 characters could not have been overlooked by the most inexperienced 

 observer. We must conclude, that M. Desmoulins, in drawing his 

 remarks from different specimens, has confounded together shells of 



