INVERTEBRATE PALAEONTOLOGY. 07 



i . i in o p s i s i> si i' v u 1 a , M. & h 



Plate 28, ligs. 17, «, b, e. 



Pectunculina purrula, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 8fi. 

 Limopsin parrula, Meek and Hayden (185(3), ib., 285. 



Shell very small, obliquely rhombic-suboval, moderately compressed; 

 anterior side rounded, usually a little more prominent above than below ; 

 base forming a rather broad curve, sometimes nearly straight in the middle; 

 posterior side obliquely truncated above, and more or less narrowly rounded 

 below ; pallial margin faintly crenulate within ; hinge somewhat arched on the 

 inside, generally equaling nearly half the length of the shell, and provided 

 with three or four teeth on each side of the small triangular pit for the recep- 

 tion of the ligament ; cardinal area small, but well denned ; beaks moderately 

 elevated, pointed, and incurved at right angles to the hinge, located slightly 

 in advance of the middle. Surface marked by fine lines and occasional 

 stronger marks of growth, crossed by exceedingly obscure, fine, radiating, 

 subpunctate striae, which are usually nearly or quite obsolete on the anterior 

 part of the shell. 



Length, 0.23 inch; height, 0.20 inch; convexity of the two valves, 0.14 

 inch. 



The radiating lines are more distinct on the inside of the shell than 

 without, especially on the middle and posterior portions, where they corre- 

 spond to the crenulations of the border. They are not very distinctly punc- 

 tate, but, under a good magnifier, seem to be slightly, though not regularly so. 

 Generally speaking, the radiating lines are not visible without the aid of a 

 lens, and often appear quite obsolete over the whole surface. 



At a first glance, this little shell is apt to be confounded with Cardium 

 rarum of Evans and Shumard, with which it is often associated. In form, 

 and many of its other characters, it is very similar to L striato-punctata of 

 the same authors ; but it presents a very marked difference in point of size, 

 the latter being near four times as large as the largest specimens among 

 hundreds of this species in our possession. The radiating striae are also much 

 more distinct on L. striato-punctata than the species now before us.* 



* I have never seen the original type of L. striato-jninctuta, nor had I, at the time of writing these 

 remarks, seen any specimen agreeing with the description of the same. Since the foregoing remarks 

 were sent to the printer, however, a perfect example, from near the Black Hills, agreeing almost exactly, 

 in size, proportions, and surface-markings, with the description and measurements of that shell, was 

 sent to me by a friend. On comparing this with our specimens, it is found to present the additional 

 difference of having an undefined shallow sulcus extendiug obliquely forward and downward from the 

 anterior side of the beaks to the front margin, to which it imparts a slightly sinuous outline. 



13 H 



