XXxii CLASSIFICATION. 



Shell circular or elliptical in section, without longitudinal sculp- 

 ture, with close and fine obliquely encircling wrinkles throughout or 

 on the posterior portion. 



Type D. unclulatum Miinster. 



Distribution, Carboniferous to Trias. 



An apparently extinct group, differing from Fustiaria Stol.in the 

 far closer oblique grooves with convex, rib-like intervals, and, so 

 far as known, no apical cleft. It is especially characteristic of the 

 early and middle Mesozoic. There are numerous species, such as 

 D. xindulatum Miinst., spitiense Guembel, tceniolatmn Sandb., annu- 

 latum Sandb., dunkeri P. & S., te7iue Miinst., etc. 



Besides the foregoing subgenera, the following groups have been 

 based upon fossil species, but they hardly seem to possess characters 

 sufficient for subgeneric rank. 



Subgenus Gadilina Foresti, 1895. 



Bull, della Soc. Malac. Italiana, xix, p. 259. 



Shell smooth and slender, imperfectly triangular in section, the 

 concave side flattened, convex side rounded. Type Z), triquetrum 

 Brocchi. Lower Miocene (Elvesian) of Piedmont. 



The recent D. insoUtum E. A. Smith (see p. 109) probably falls 

 into this group, though in it the subgeneric peculiarities are less ac- 

 centuated than in the Piedniontese fossil. 



Foresti thus defines the group, which he ranks as a subgenus of 

 Siphonodentalium : Shell triangular in section throughout, not 

 swollen in the middle ; posteriorly tapering and curved ; smooth ; 

 slightly contracted and distinctly oval toward the anterior aperture, 

 simple and entire at the posterior orifice. 



Section Coceodentalium Sacco, 1896. 



Boll. Mus. Zool. ed Anat. Comp. K. Univ. Torino, xi, p. 98 ; Moll. 

 Terr. Terz. Piem. e Ligur., xxii, p. 110, 



Shell longitudinally costulate, the ribs strongly granose; apex as 

 in the D. novemcostatum group o^ Antalis. Type i). radt( /a Schroter. 



This group, which we would hardly be disposed to individualize 

 by a subgeneric name (see p. 29), comprises besides its type D. rad- 

 ula of the Piedmont Upper Miocene (Tortonian), a few recent spe- 

 cies such as D. carduus Dall, its probable ancestor Z>. callioglyptmn 

 Pils. & Sharp of the San Domingo Oligocene, and D. Tryoni Pils. 

 & Sh. of the same beds. 



