230 University of Texas Bulletin 



EXOGYRA Say 



EXOGYRA HAARMANNI sp. nov. 

 PL 18, figs. 4-8 



In the lowest beds of Cerro del Macho numerous specimens of an en- 

 tirely smooth Exogyra have been found. This species resembles to a 

 certain degree Ex. columba Lamarck but is not completely identical with 

 it._ Its character is : 



Larger valve thin, very convex, especially in the central portion, thus 

 forming a kind of rounded crest which goes from the beak to the lower 

 margin. This crest gives the shell an asymmetric aspect because it is not 

 entirely in the center, but a little nearer the anterior margin ; this asym- 

 metry is particularly noted in large specimens and much less in juvenile 

 individuals. The beak is quite slender, spirally coiled at its point. The 

 valve is broad, without forming wings and without a furrow in any of 

 the sides. From the above mentioned crest the shell slopes rapidly toward 

 the anterior margin and slowly toward the posterior margin. The sur- 

 face is entirely smooth, showing only fine striae of growth and in a large 

 specimen there is an indication of two slight concentric ridges, certainly 

 produced by the manner of growth. 



The smaller valve is nearly flat. In none of the specimens is the surface 

 entirely preserved and a detailed description of this valve can not be made. 



Oar species resembles Ex. columba Lamarck but is much smaller and 

 never shows a radial ornamentation, and the rounded crest is nearer to 

 the anterior margin while in the European species it is nearer the posterior 

 one. 



In its shape our species resembles still more Ex. columbella Meek, 1 

 especially on account of the position of its crest, but the radial ornamenta- 

 tion of that species is entirely missing in ours. 



Number of specimens : 12 and numerous fragments. 



Age: Upper Cenomanian?, lower beds of Cerro del Macho. 



EXOGYRA cfr. OLISIPONENSIS Sharpe 



1850: Exogyra olisiponensis Sharpe, Secondary Distr. of Portugal, p. 185, pi. 19, 



figs. 1, 2. 

 1911 : Exogyra olisiponensis Woods, Cret dep. Northern Nigeria, p. 278, pi. 20, figs.1-3. 



cum syn. 



In the upper part of the marls which we believe belong to the Ceno- 

 manian, Dr. Haarmann found a fragment of a large Exogyra. This 



'Stanton, Colorado Form., p. 63, pi. 8, figs. 2-4. 



