52 



BULLETIN OF THE LABORATORIES 



a deep byssal sinus and steep umbonal slope. Length of left valve 

 1-6 mm; width 15 mm; length of hinge 10-12 mm. 



Nodule layer, Moot's run. ("ollection of W. F. Cooper. 



Auicul opecten (Cf. oiveni, M. and W.) 

 fPlate III, Fig. 5.) 



Shell small, subcircular. lower margin nearly equally curved to 

 points nearly half way to the beak, here suddenly flexed to meet the 

 lateral margins, the anterior one in the left valve being slightly con- 

 cave, the posterior a little convex; beak prominent; hinge line some- 

 what less than the width ; anjerior ear rather large, obtusely angled ; 

 posterior ear smaller and more acute and rather less sharply defined ; 

 surface quite convex, greatest convexiiy being about one-third from 

 the beak, ornamented by rather numerous bifurcating and implanted 

 striae, of Avhich about fifty can be counted on the body of an average 

 shell. Length 10 mm ; width 10 mm ; length of hinge 8 mm. The 

 difficulty of comparing this species with A. oweni is increased by a 

 doubt as to which valve is figured by Meek and Worthen. The de- 

 scription states "right valve unknown," while the figure is stated to 

 be that of the right valve. If it be a left valve and our own are like- 

 wise left valves, the relation of the ears is reversed. Our species is 

 smaller, but otherwise resembles the Illinois form. None of the spe- 

 cies quoted by Winchell as from the Waverly and its equivalents, 

 seem to be identical with this, though it may prove the young stage of 

 one of the common ones, perhaps A. winchelli. The horizon is the 

 same as in that species, the free-stone of middle Waverly. 



Avicidopecteiv (Cretiipscteii) newarhensis, ^^'™- ? 



(Plate III, Fig. 31.) 



A single right valve may belong to this species as indicated by its 

 rather narrow form. As VVinchell's specimens were all left valves, the 

 identification can only be conjectural. Length 18 mm ; width 15 mm. 

 Valve very flat, covered by irregularly alternate, rather filiform striae, 

 Umbonal slopes about 90° or less. 



