Descriptions of Species. 31 



umbone ; posterior umbonal margin elongate, sloping posteriorly 

 at an angle of about 30 degrees from tbe umbone; this margin 

 is straight when viewed laterally, but bends strongly outward 

 toward the gaping posterior margin, with which it unites by a 

 gentle curve; surface marked by strongly rounded ribs and 

 grooves, subconcentric, sinuous and uniting with each other at 

 a common groove which is parallel with the anterior margin. 



Only a single poorly preserved cast of a right valve of this 

 species has been found, the anterior portion of which is not 

 visible. It was collected in the heavy conglomerate which 

 marks the base of the Comanche Series at its contact with the 

 Carboniferous formation, on Sycamore creek, Burnet county, 

 Texas, near the crossing of the Burnet and Travis Peak roads. 

 The species is named for Dr. Otto Lerch, of the Louisiana State 

 Geological Corps, who, as a Texan, has made valuable contri- 

 butions to the knowledge of his State. 



Pleuromya (?) henselli sp. nov. 

 Plate IV, Figs. 1, 2. 



Shell elongate-elliptical ; length, three and one-quarter inches ; 

 "height, two inches ; umbones anteriorly subcentral, round, and 

 not prominent; anterior margin strongly rounded, continuing 

 by curvature into the pallia! margin ; pallial margin elongate, 

 slightly curved ; posterior margin sub-truncate, slightly gaping ; 

 anterior umbonal margin sinuous, slightly gaping ; posterior 

 umbonal margin about one-third longer than anterior ; interior 

 and hinge mechanism not seen. 



The generic position of this species is very doubtful ; but, in- 

 asmuch as it is one of the most characteristic casts of the Glen 

 Rose beds in the Colorado River section, it is important that it 

 should be here figured. The species has a resemblance to Thm- 

 cia my<r/ormis White, but differs in some details. 



Isocardia (?) medialis (Conrad). 

 Plate II, Figs. 4, -5; plate III, Fig. G. 



Cardium mediale Conrad, U. S. and Mexican Boundary Report, 

 vol. i, p. 149, plate iv, figs. 4a, b. 



Conrad described this form as follows : 



" Cordate equilateral, ventricose,; base profoundly and nearly 

 regularly rounded ; beaks prominent; posterior margin truncated, 

 direct." 



