106 Hill The Invertebrate Fossils of the 



I have observed only a few specimens. These occur with 

 great scarcity in the Caprina limestone, in association with 

 Radiolites davidsoni at Belton and near Austin. The species is 

 named in honor of Mr. T. V. Munson, of Denison, Texas. 



This species resembles in general form the excellent figures of 

 0. Joanfe Choffat, from the Cretaceous of Portugal. 



Radiolites davidsoni sp. nov. 

 Plate XIII. 



Description of Figured Specimen. Very elongate, measuring over 

 40 centimeters ; slightly flaring at larger end and gently tapering 

 to small extremity; somewhat sinuous, pointed, and attached 

 at lower end ; exterior surface strongly marked by longitudinal 

 ribs and grooves, as follows : Two especially broad and conspic- 

 uous grooves extending the entire length of the shell on oppo- 

 site side to that shown in large figure, but seen in small segment 

 and end view. These are accompanied by two large corre- 

 sponding oblate ribs and a sharp, angular carina. These two 

 grooves, ribs, and carina occupy one of the sides of the sub- 

 triangular circumference. The carina is very prominent and 

 sharp, and extends from the smaller end to within about ten 

 centimeters of the large extremity, where it becomes exfoliated 

 and deflected like a mantle over and across the large ribs and 

 grooves. This carina forms the upper margin of the large 

 figure, and the angles seen in the cross-sections, and is opposite 

 the smaller angle of the semi-lunate interior. It is bordered 

 upon one side by one of the major grooves above described 

 and upon the other, by the somewhat flattened face shown in 

 the figure of larger cross-section, on Plate XIII. The remaining 

 two-thirds of the surface of the shell is marked by about fifteen 

 small linear ribs, separated by wide, slightly concave depres- 

 sions. Interior of shell a hollow cavity subpyriform or semilu- 

 nate in cross-section, and marked by a few widely separated 

 concave partitions occurring at intervals of three to five centi- 

 meters. Opposite the left hand major groove there is a slight 

 projection extending tlie length of the interior which makes a 

 narrow sinus in the casts when found. The interior is usually 

 filled with calcite crystals. 



Shell, irregularly thick, varying from three-quarters to one- 

 half centimeter in different parts'of the circumference. Outer 

 surface is very smooth between the flutings and marked by fine 



