16 bulletin: Ml'SEUM OF COMPARATIVE ZOOLOGY. 



Parastrophia. which, differing in many respects from the ori^nal 

 ^'mens mav perhaps, considering the vanabihty of the members 

 o?Thr^nus. be Inckuied in the Minnesotan group, as a speaes rather 



''''^u.Znl^ Schuchert state that their variety is "distinguished 

 .n g the length and width nearly equal, the valves more convex 



^dh plications somewhat n.ore pronounced m the foW and s.^ 

 and U-s numerous in the lateral portions of the shell. No further 

 de c iption is given, but the single specimen figured is large (15 mm^ 

 long) has three broa.l plications on the fold, two m the smus, and a 

 nair on either side of the fold and smus. 



^ The three specimens found at Martinsburg are fully as convex as 

 the Minnesota':^ specimen, but the largest is only 10 mm. long^^and 

 all have more and narrower plications m the fold and smus. Two of 

 them have four plications on the fold and three m the ^^^^^^ ^^^ ^^e 

 third the largest, has four in the sinus. Two o them have two and 

 one of them three plications on each side of the fold and smus. 



This rather detailed description is given because of the mcreasmg 

 necessitv of more definite knowledge of the limits of variation, and 

 the possibility of distinguishing species of Parastrophia. 



Parastrophia hemiplicata Hall. 

 Alrypa hemiplicata Hall, Pal. N. Y., 1847, 1, p. U4, pi. 33, fig. 10. 



To assist in a study of Parasirophia hemiplicata which must ulti- 

 matelv be made, it is worth while to record the characteristics of any 

 specimens whose horizon is definitely known. Fourteen specimens 

 were found in the lower thirty feet of the Trenton, but a number of 

 these were too poorly preserved to yield any satisfactory information. 

 The following table shows the principal characteristics: 



