BULLETIN NO. 2. 21 



AVICULOPECTEN MONROENSIS. (sp. nOV.) 



Shell below the medium size, left valve moderately convex, sub- 

 ovate or nearly circular below the ears, the lateral borders grad- 

 ually rounding into the broadly rounded basal margin. Ears nearly 

 equal in size and ornamented with live or six radiating costse 

 similar to, and continuous with those on the body of the shell, 

 and also with delicate concentric lines that are plainly visible 

 under an ordinary lens. Surface of the valve ornamented with 

 60 to 70 n-regular sized rounded costal that are usually a little 

 wider than the intervening spaces, and fine transverse stride sim- 

 lar to those on the ears, which are only visible under a lens. 

 A right valve belonging apparently to this species is nearly flat, 

 radiating costse very fine, anterior ear longer than the other and 

 defined by a deep narrow sulcus, and both ornamented with costse 

 and concentric striae that are a little less conspicuous than those 

 on the opposite valve. 



Length of left valve ii inch ; breadth about the same ; length 

 of hinge line W inch. 



Position and locality: Oolitic beds of the St. Louis group, 

 Monroe county. 111. 



No. -2509 of the Illinois State collection. 



Collector, A. H. Worthen. 



AVICULOPECTEN TALBOTI. (sp. IIOV.) 



Associated with the A. Monroensis, there is a smaller form that 

 seems to be clearly distinct, and may be characterized as follows : 



Shell small, broadly ovate in outhne, left valve moderately con- 

 vex, ears short and not well defined from the lateral borders. 

 Surface apparently smooth, but under a good lens minute radi- 

 ating and concentric lines, may be seen, which are most conspicu- 

 ous on the ears and lateral borders of the shell. 



Length of the largest individual seen ^ inch ; breadth about the 

 same ; length of hinge line about ^ of an inch. This form differs 

 from the A. Monroensis in its smaller size and nearly smooth 

 surface. Named in honor of my friend Henrv Talbot, Esq., of 

 Waterloo. 



Position and locality: Same as the last. 



No. 2510 of the Illinois State collection. 



Collector, A. H. Worthen. 



AVICULOPECTEN COLLETTI. (sp. llOV.) 



Shell beloAV the medium size, inequilateral, ovate. Left valve 

 slightly convex, ears well defined and unequal in size. Anterior 

 ear small, triangular, posterior ear rather larger than the anterior, 

 ornamented with four or five longitudinal costfe and fine trans- 

 verse lines of growth, with a well defined notch at its junction 

 with the lateral border. Lateral borders straight nearly to the 



