New Species of Pal/eozoic Fossils. 175 



cular scars of ventral valve elongated and bounded by sharp 

 ridges that leave three grooves extending beyond the middle 

 of the shell in the exfoliated cast, middle groove deeper than 

 the other two, and extending in some instances almost to the 

 front margin; sometimes the middle groove widens from the 

 beak to about the middle of the valve, then narrows abruptly 

 and is continued toward the front as a slender furrow. Mus- 

 cular markings on dorsal valve very variable; in general, the 

 scars were long and separated by a narrow carina. The 

 other details, however, are far from being constant. Dental 

 laminaj forming two short septa in umbonal cavity of ventral 

 valve, nearly parallel or sHghtly diverging where their lower 

 margins join the shell, but curving at their upper margins so 

 as to conform nearly in direction to the lateral margins of the 

 deltidial plate. Surface smooth, marked only by obscure lines 

 of growth. Shell very finely punctate. Internal loop un- 

 known. 



V^ery common in beds of the age of the Hamilton period, 

 associated with S'pirifera fan- y ana, S. undifem^ Cyrtina ha7n- 

 iltonensis, Atryfa retiadaris and other characteristic species, 

 at one locality near Fayette, Iowa. 



Large specimens are an inch and a quarter in length, more 

 than an inch in width, and three fourths of an inch in thickness. 

 Immature forms are very common. 



In none of the specimens have I been able to find any traces 

 of the internal loop. The shells in a large proportion of cases 

 are hollow, the cavity being lined with crystals of calcite. 

 The elongate muscular impressions are characteristic of the 

 genus Cryptonella, as described by Professor Hall in the Fif- 

 teenth and Sixteenth Annual Reports on the State Cabinet of 

 New York, and in the fourth volume of the Paleontology of 

 New York, but whether the calcareous loop possessed the 

 distinguishing characteristics of that genus has not been de- 

 termined. 



For some time I was incHned to regard the specimens from 

 Fayette as merely large forms of Terebratula Imckloeni, Hall, 



