INSTITUTE OF SCIENCE, PHILADELPHIA. 3T9 



of which the type is HI. quadricarinata Brocchi. It differs from Tuba s. s. in 

 being more slender, and in having the sinistral nucleus not immersed, or only 

 partially so, and in having more whorls in the nuclear portion, and, so far as 

 I have been able to discover, in these particulars only. 



Gegania is an absolute synonym of Tuba ; both have a sinistral nucleus, 

 which is, however, so far immersed, or of such small coil, as to appear to a 

 casual examination merely gibbous and dextral. I have verified this fact by 

 most careful study of the typical specimens of Lea and Jeffreys. 



The section Acroccelmn Cossmann is based on a species which has the 

 nuclear whorls, as shown by his figure, horizontal, capping the spire with the 

 actual apex immersed, instead of projecting as in Mathilda, or immersed at 

 top of a conical coil as in Tuba. 



The sinistrorsity of the nucleus in Gastropods is of less systematic value 

 than formerly supposed. Many species of Calliostoma have a reversed nu- 

 cleus without differing in other respects from their congeners. If the true 

 nucleus is so short as not to form a coil, it is obvious that the tendency which 

 would have made a coil sinistral if it exists will be so masked as to be barely 

 recognizable, or not at all. That this is often the case, I have fully satisfied 

 myself For this reason I am unable to accept the valuation placed by some 

 excellent authorities on this feature. In the present case it may be said that 

 the genus Tuba and its sections Mathilda and Acroc(Eluni have a nucleus 

 of which the initial tendency is sinistral, but in which this tendency is realized 

 in a sinistral coil exposed to view and vertically tipped aside only in Mathilda, 

 while in Tiiba s. s. the coil is very short and mostly immersed in the subsequent 

 apical whorls, and in Acroccebtm a coil is probably not formed, the apical 

 point of the nucleus being simply immersed. 



In all the species there is an effuse tendency at the base of the pillar 

 recalling Tricliotropis , but which is emphasized by a slight thickening on the 

 pillar only in rare cases. Still, some of the species, or some specimens in some 

 of the species, do show such a slight callosity, like the one about to be de- 

 scribed. This feature is more likely to be found in those species with a strong, 

 straight pillar and strong basal spiral sculpture than in those like Tuba att- 

 tiquata, in which the basal sculpture is faint and the aperture more orbicular. 

 In short, this character is dynamic and analogous to that exhibited by Pyr- 

 gida anmdata, which for the same reasons exhibits an effuse aperture, though 

 belonging to a group in which the aperture is normally entire in front. 



Tuba acutissima n. s. 

 Plate iS, figure 4 a. 

 Miocene of the Chipola epoch, in the lower bed at Alum Bluff, Chatta- 

 hoochee River, Northwest Florida ; Burns. 



Shell with eight or nine rapidly enlarging whorls ; nucleus minute, de- 

 •coUate in all the specimens, but from the slenderness of the subsequent whorls 



