GASTR<>mi>A. 



in casts; sides gently convex to the edge of the umhilicu> into which they descend 

 ;it lir>t nither abruptly, then gently, the ventral part spreading saddle-like over the 

 inner volution. \i>erture subcordate, notched below; outer lip rather broadly and 

 deeply emarginatod. Umbilicus about :." nun. wide in a specimen 8 mm. in 

 diameter, narrowly rounded at the edge. Surface of casts with distinct, subregular, 



lly curved, transverse stria-, aveni^in^ about live in 2 mm. on the sides and 

 Lark. Tin- stria- continue over and are quite distinct and curved on the flattened 

 dor-inn or slit-band. On the latter some very fine revolving lines are faintly dis- 

 tinnuMiahle. Somewhat oblique and stronger revolving lines, about four in 1 mm., 

 occur on the sides of the volutions. Greatest diameter of a large specimen 8.3 mm; 

 wi.it li of aperture 5.0 mm.; hight of same 5.0 mm. 



The original description ami figures are incorrect where they differ from the 

 present work on the species. It is scarcely necessary to go into details. 



i if American fossils we can compare this pretty shell only with species of 



elites and possibly of Iliicani-i. < ijiiolUes retrorsus and C. carinatus are found with 

 it. Imt 1'ntli have more volutions, are sharply keeled and without a slit-band. The new 

 < 'ijrtolitts jMirvus is also associated and, because of \\< small si/e and relatively coarse 

 markings, is more likely than any other fossil known to us to be confused with C. 

 nid'liiln: still, they may be readily distinguished, C. parvus having the usual sharp 

 dorsum and wider subquadrate aperture. Besides, it should be borne in mind that 

 they are testiferons specimens and not casts of the interior of the species of 

 CyrtolHes mentioned that look like casts of Cyrlolitinn nHi<lul<i. Casts of CyrtolUes 

 never show an imprint of the surface ornamentation, but those of the Cyrtolitina, on 

 the contrary, are very distinctly marked. 



formation and locality. Upper part of the Trenton group, | n the river <|uarrlM tint went of Oor- 

 iiiKUm, Kentu. 



CWI*ioi.-E. O. Ulrich. 



ienus PKOTOVVARTHIA, n. gen. 



Belierophon (part.), of numerous authors. 



For generic characters see page 848. 



The, chiefly Lower Silurian, group of shells for which this genus is proposed is 

 -trikingly similar to the I'ermo-Carboniferous species embraced in Waagen's genus 

 H'.ir/AiVi. Indeed, there is little more than a single character, and that possibly is 

 not always well developed, which distinguishes them. In /'/-..'/,</ ,irthi<i, namely, the 

 inner lip is prolonged as a thin grano-lineate sheet around the umbilical regions 

 and over a greater or lesser portion of the dorsum of the posterior end of the last 

 volution. Nothing of this kind has been observed in \\'arthin. That the surface of 



