Wetter — Kinderhook Faunal Studies. 161 



Length of an average example 6^ mm., breadth 6^ mm., 

 convexity of pedicle valve 3 mm. 



Remarks. The size of this species varies somewhat, the 

 measurements given above being taken from a medium-sized 

 individual. The largest specimen observed has a length of 

 9 mm. 



Productus mokbillianus Win. 



PL XIV. f. 24-25. 



Original description. st Shell small, transversely subellip- 

 tic, only moderately produced. Hinge line seven-eighths the 

 greatest width of the shell; ears small, nearly right-angled. 

 The shell regularly contracts from the aperture to the beak, 

 which is small, subacute, and projects slightly beyond the 

 hinge. The arching of the shell is such that when resting on 

 the aperture the greatest height is equal to one-half the 

 greatest width. No sinus or flattening present. The sur- 

 face is marked by a series of deep, continuous, equidistant 

 wrinkles, ten or eleven in number, becoming obscure toward 

 the beak ; between the wrinkles are numerous tine concentric 

 striae not easily seen without a magnifier. These features 

 are crossed by a longitudinal system which, near the beak, is 

 a set of fine regular costae, which near the middle become 

 interrupted by the wrinkles, and, losing their identity, result 

 in several concentric bands of short longitudinal tubes buried 

 in the substance of the shell, and gradually emerging and 

 presenting their apertures anteriorly." 



Width of specimen illustrated 29 mm., length 26 mm., 

 greatest convexity 1\ mm. 



Remarks. The original description of this species was 

 made from a specimen coming from the base of the Burling- 

 ton limestone at Burlington, Iowa, but another specimen from 

 bed No. 5 is said to be "probably identical with this." This 

 sandstone specimen mentioned by Winchell is preserved in the 

 ' k White Collection" with the label marked " Type in part," 

 and it is this specimen which is here illustrated and whose 

 dimensions are given. Judging from the dimensions given 

 by Winchell, this specimen is about twice the size of that 

 from the base of the Burlington limestone, and its relative 

 convexity is only about one-half as great. 



