454 MISSISSIPPIAN BRACHIOPODA 



NUCLEOSPIRA ROWLEYI n. Sp. 



Plate LXXXII, Pigs. 43-48 



1901. Nuclcospira barrisi Rowley, Am. Geol., vol. 27, p. 350, pi. 28, figs. 



46-48 . ( Not N. barrisi White ) . 

 1908. Nucleospira barrisi Rowley, Mo. Bureau Geol. and Mines, vol. 8, 2nd 



ser., p. 85, pi. 18, figs. 25-27. 



Description. Shell small, lenticular, usually a little wider than long, 

 subcircular or transversely subelliptical in outline, the greatest width 

 near the mid-length of the shell, the hinge-line much shorter than the 

 greatest width, the cardinal extremities rounded. The dimensions of a 

 nearly perfect example are: length of pedicle valve 4.5 mm., length 

 of brachial valve 4.1 mm., greatest width 5 mm., thickness 3 mm., length 

 of hinge-line 2.3 mm. 



Pedicle valve most convex posterior to the middle, the surface curving 

 abruptly to the cardinal margin, and more gently to the lateral and an- 

 terior margins; mesial sinus originating in the umbonal region near the 

 beak, very shallow, rather broad, not sharply defined at any point but 

 becoming more ill-defined anteriorly; beak short and obtuse, but slightly 

 incurved; cardinal area small, concave, the lateral margins defined by a 

 slight angularity of the surface separating the surface of the lateral slopes 

 of the valve from that of the cardinal area. Surface of the valve appar- 

 ently smooth or marked only by obscure concentric lines of growth, in 

 most individuals, but in the best preserved examples the presence of nu- 

 merous, minute, crowded, appressed spines is shown. 



Brachial valve a little less convex than the pedicle, the greatest convex- 

 ity near or a little posterior to the middle, the surface curving a little 

 more abruptly to the posterior than to the lateral and anterior margins; 

 mesial portion of the valve depressed in a narrow and shallow sinus in 

 the umbonal region which merges anteriorly into a rather broad, ill- 

 defined, flattened band, scarcely or not at all depressed below the general 

 surface, and continuing to the front margin ; beak obtuse and only slight- 

 ly incurved, the umbonal region scarcely protuberant beyond the cardinal 

 margin posteriorly. Surface of the valve apparently smooth or marked 

 only by obscure concentric lines of growth. 



Remarks. This little shell has sometimes been incorrectly identified 

 as A T . barrisi, but besides occurring in a very different horizon than that 

 species, it is a much smaller shell. The largest example of the species ob- 

 served by the writer is under 7 mm. in width, and in this specimen the 

 width has been increased by distortion. 



Horizon. Louisiana limestone. 



