56 COLORADO COLLEGE STUDIES. 



Occurre)icc. — In the Duck creek limestone, on Duck creek, 

 between one and two miles ncn-theast of Denison, Texas. 



This fossil is much less common than the I .comancheana.* 

 The specimens occur as casts, with occasional remnants of 

 the shell. , 



The species is named after Mr. J. T. Munson, of Denison, 

 in recognition of the generous aid which he has shown him- 

 self every ready to lend to scientific research. 



NUCULA CHICKASAENSIS, sp. UOV. 



Shell small, of moderate convexity, though more convex 

 than that oi N.caflterina »o?;/s, ovate-triangular, the anterior 

 side descending directly and subvertically from the low. nearly 

 terminal beaks, giving the anterior part of the profile an 

 obliquely truncate appearance, posterior cardinal side slightly 

 convex, posterior extremity somewhat narrowly rounded, base 

 long, gently convex, and suddenly curving upward at its 

 anterior end; shell divaricately ornamented with tine and 

 close raised lines and strite, each of which has the apex of its 

 V-like angulation directed toward the beak, the anterior arms 

 of the Vs being gently concave toward the anterior, or supero- 

 anterior part of the shell, the posterior arms presenting a 

 gentle concavity upward and backward, the angle of divarica- 

 tion, at apex, somewhat less than a right angle. 



Measurements. — Height 11.5, length 14, breadth 8 mm. 



Occurrence. — The type of this species was collected by 

 my wife from the Comanche Peak limestone, overlooking 

 Little Hickory creek south of Overbrook in the Chickasaw 



* The writer would here note that tbe species, "/nocejYimMS muUisirUitxis" vih\c\i 

 he published in his "( "ontribut iou to tlie Invertebrate Paleontology of the Texas Creta- 

 ceous," is invalid, having been based on a mutilated specimen of Avicula pedernalis, 

 as he discovered when, on his expedition of July to September, 1S93, he collected 

 specimens of the latter fossil, no specimen of wliich, sufficiently well preserved to be 

 oa.sily recognized by one not previously acquainted with tlie .species, had been avail- 

 able for his study in the museum of the State Geological Survey prior to his leaving 

 Austin. Not suspecting the former presence of the largo wing, which had boon 

 broken off, on the imperfect specimen examined, the writer was led to refer this 

 specimen to the genus Inoceramus, in view of its transversely fibrous shell-structure 

 and of its degree of resemblance in form to Inoceramus sublwvis, overlooking the 

 fact that the shell of Avicula also has such structure. 



