142 Anxals of iHF. Carm:(;ie Muskim. 



Adult. — In the adult state the valves are about equally convex and 

 bear from lo to 26 pairs of plications. The cardinal extremities are 

 acute, but are not prolonged into the spiniform extremities as in the 

 neanic stages. The shells are of a wide type, with a high index, 2.25 

 to 3.00. The front is regularly curved. The fold is broad and 

 marked by a deeply impressed line and there is a distinct plication in 

 the sinus. The surface is covered with concentric lamellae of growth 

 which, in old specimens, are so prolonged on the plications as to 

 give the surface a spinose character. Three individuals, or one per 

 cent, of the whole, show senile characters in the thickening of the 

 shell, the spinose surface, and great number of growth lines toward 

 the front. 



Co)iipa7-isou with fJic Same Species from Ot/ie?- Localities. 



Specimens from Cherry Valley, Otsego Co., have about the same 

 form as those from the present material. The cardinal extremities are 

 acute, but not far extended, and the front is regularly curved. The 

 specimens are large ; 13 to 17 mm. long and 40 to 58 mm. wide, and 

 have a relatively small number of plications, 24 to 40. The index 

 varies from 2.35 to 4.46. The specimens do not show the depressed 

 line in the fold or the plications in the ventral sinus. Specimens 

 from Worcester, Otsego Co., from the collection of Miss Grace 

 Goodenough, show two forms, one short, wide form like the speci- 

 mens from Canandaigua Lake, and a long form with a very low index 

 and rather blunt cardinal extremities. Specimens of both types show 

 the depressed line in the dorsal fold and most of them have the plica- 

 tions in the sinus of the ventral valve. A small specimen of the short 

 type is 6 mm. long and 29 mm. wide and has 32 plications. A large 

 specimen of the .same type is 19 by 66 mm. with 50 plications. The 

 index varies from 2.81 to 4.83 among individuals of this form. 



A large s])ecimen of long form is 28 mm. long and 35 mm. wide, 

 and has 40 i)lications, while a small individual is 9 by 12.5 mm. with 

 26 plications. The index in this tyi)e of shell varies from 1.25 to 

 1.60. 



The specimens from East Bethany belong to the .same type as those 

 from the silicified material and have about the same range in size and 

 in number of plications. The index varies from 2.00 to 3.69; the 

 plications from 14 to 40; the length from 7.5 to 19; and the width 

 from 1 5 to 60 mm. All of the 62 specimens from this locality have 



