Wetter — Kinderhook Faunal Studies. 157 



pointed beak, having three plications in the sinus; a less 

 common form being much thicker with the sinus produced 

 into a lingual extension at the front of the shell. This last 

 variety approaches very closely to Rhynchopora pustulosa, 

 but the shell structure is not punctate as in that species. The 

 little specimen described by Winch ell as Rhynchonella unica 

 (see Plate XIII. figs. 7-8) is only a small distorted specimen 

 of this species, its peculiar characters being due to the lateral 

 crushing of the type specimen. 



Khynchopora pustulosa (White). 



PI. XIII. f. 4-6. 



Original description. " Shell subtrigonal or subglobose, 

 front broadly rounded or slightly flattened, sides flattened and 

 meeting at the beak at nearly a right angle. Brachial valve 

 much more convex than the pedicle valve, which is usually 

 somewhat depressed ; beak closely incurved, highest part 

 near the front margin. Beak of pedicle valve prominent, 

 acute and considerably incurved ; delthyrium triangular. 



" Surface marked by from twelve to sixteen strong, some- 

 what rounded plications, three of which are usually mod- 

 erately depressed on the pedicle valve, and four elevated on 

 the brachial valve, forming the mesial fold and sinus, which 

 are not observable much more than half the length of the 

 shell. Along the center of each of the plications, for a 

 considerable distance from the margin, runs a slight de- 

 pression, giving them a flattened appearance. 



" Fine concentric striae and imbricating lines of growth 

 are visible on well-preserved specimens. When the shell 

 is partially exfoliated it usually presents under the lens 

 a fine pustulose appearance." 



The dimensions of a rather large specimen are : length 

 12 mm.; breadth 14 mm.; thickness 10 mm. 



Remarks. The types of this species closely resemble 

 some individuals of C amarotoechia 9 heteropsis, and from 

 the form of the shell alone it would probably be imprac- 

 ticable to separate these two species. All the authentic 

 specimens of this species, however, exhibit the finely punc- 

 tate shell structure of Rhynchopora, while authentic 

 specimens of C. heteropsis are apparently impunctate. 



