NIAGARA FALLS AND VICINITY 20/ 



resiliiun occurs, which is lodged in special grooves or pits. The 

 scars marking the attachment of the adductor or closing muscle 

 or muscles, vary greatly, and are frequently preserved in the fossil 

 forms. When two are present, they are designated, respectively, 

 the anterior and posterior adductor scars. The line of attachment 

 of the fleshy mantle which builds the shells, i. e. the pallial line, 

 is often visible. Near the posterior end it frequently makes a re- 

 entrant curve — the pallial sinus — indicating that the animal had a 

 retractile siphon. The various parts described are indicated in fig. 



134. 



The principal soft parts of the animal comprise: the mantle, con- 

 sisting of two fleshy folds, one lining each valve, and building it; 

 the abdomen, with the anteriorly placed month, and the antero-ventral 

 foot; the gills, or branchiae, which consist of complicated lamellae 

 hanging on either side of the abdomen in the mantle cavity; and 

 the siphons — present only in certain forms — posteriorly placed, often 

 capable of great extension, and serving, the one for the entrance 

 of the water and food particles, and the other for the exit of the 

 water and waste products. 



Genus pterinea Goldfuss 



[Ety. : TiTepov, wing] 



(1826. Petrefacta Germaniae, p. 133) 



Shell inequivalve, inequilateral; posterior side w^inged, anterior 

 end nasute or with a well defined ear. Ligament internal; Hga- 

 mental area longitudinally striated. Cardinal teeth two or more; 

 lateral teeth linear oblique. Posterior muscular impression large, 

 situated on the post-umbonal slope; anterior muscular impression 

 small, situated within the rostral cavity. Test ornamented with rays. 



Pterinea emacerata (Conrad) (Fig. 135). Avicula ema- 

 c e r a t a Conrad (Hall. 1852. Pal. N. Y, 2:228, pi. 59) 



Distinguishing characters. Moderately 

 oblique; large and posteriorly concave 

 wing often extending beyond the shell 

 below; small anterior ear; flat, smooth 

 right valve with striated wing; convex 

 left valve, with strong radii, interrupted 



by fainter concentric striae. ^'^- ^^^ Pterinea emacerata 



Found perhaps in the Clinton shale, rarely in the lower and mid- 

 dle Rochester shale and abundantly in the upper shale. Niagara 

 sections. Also at Lockport and elsewhere (Hall). 



