STANTON : THE MARINE CRETACEOUS INVERTEBRATES. 29 



fine, closely arranged lines of growth that pass directly around the 

 shell. 



The figured specimen measures 55 mm. in length and 7 mm. in diam- 

 eter at the larger end. The test itself rather thick and the surface is not 

 well preserved on the specimen figured but another fragment shows it per- 

 fectly. None of the specimens are well enough preserved to show the 

 apertures unbroken, and the subgeneric reference is therefore uncertain. 



Locality and position. From the Ammonite (Belgrano) beds ten miles 

 east of Lake Pueyrrydon, represented by four fragmentary specimens. 



GASTROPODA. 



PLEUROTOMARIA TARDENSIS sp. nov. 



PL VII, Figs, i and 2. 



Shell large, broadly conical, consisting of not more than seven or eight 

 convex whorls ; apical angle about 90 ; base broadly rounded, not um- 

 bilicated ; slit rather broad (5 mm. in the type), extending back over 

 about one-fifth of the last whorl, situated above its middle, so that the 

 slit-band on the whorls of the spire is near the middle of their visible por- 

 tion ; aperture obliquely subovate ; outer lip simple, acute ; inner lip 

 rounded below and forming a distinct callus above, which is especially 

 prominent and thick over the umbilical region where it spreads out in a 

 broadly crescentic form ; surface marked by numerous inconspicuous 

 spiral lines, by an obscure furrow a short distance below the smooth slit- 

 band and another a little farther above it, and by rather coarse, irregular 

 lines of growth. 



The type measures 110 mm. in height (with apex of spire restored) and 

 127 mm. in greatest breadth. 



The species is based on a single specimen, which, though lacking the 

 apex of the spire and a part of the test, is otherwise in an excellent state 

 of preservation. It probably should be referred to the section Pero- 

 trochus, which Fischer established for P. quoyana Fischer and Bernardi 

 and to which he provisionally referred a number of Jurassic species which 

 have the same general features as this shell, though none of them is so 

 stout in form. No Cretaceous species known to me is so closely related 

 as to require detailed comparison. 



