xii SYNOPSIS OF THE GENERA. 



Pernnperlen* Winchdl. Shell like Pecteii. Hinge with a central cartilage pit 

 uiiii a crennlated liinge-plate on each side below the hinge-margin. This and 

 the lollow ing genus appear to be more nearly related to the genus Pecten than 

 In A \ ieidopecten. 



Crenipecten, Hall. Like Aviculopecten in form. Hinge furnished with a series 

 of small cartilage pits throughout its entire length. Examples, pi. ix, figs. 12, 15. 



Aviculopecten, McCoy, is emended to include those forms which have the hinge- 

 line usually shorter than the tran.sverse diameter, and both ears well-defined. 

 Test ornamented with rays. Example, pi. i, fig. 10. 



Lyriopecten, Hall. Differs from the preceding in the short hinge-line and 

 very small anterior ear. Test usually' ornamented with strong rays. Example, 

 pi. viii, fig. 8. 



Pten'nopecten, Hall. Hinge-line long. Ears not well-defined, being simple 

 expansions or extensions of the upper lateral margins to the hinge-line. Test 

 ornamented with rays. Examples, pi. ii, fig. 18 ; pi. v, fig. 6. 



Pterinea, Goldfuss. Shell inequivalve, inequilateral ; posterior side alate ; 

 anterior end nasute or auriculate. Ligament internal ; ligamental area longi- 

 tudinally 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 

 iirnamented with rays. Examples, pi. xv, figs. 1-21 ; pi. Ixxxiii, fig. 12. 



S. g. Veriumnia, Hall. Differs from Pterinea in having the right valve convex, 

 and the left flat or concave. Hinge area narrow. Example, pi. xxiv, fig. 12. 



Actinopteria, Hall. Characterized from Pterinea in the absence of a inroad 

 striated ligamental area and strong cardinal and lateral teeth. Right valve 

 sub-convex. Surface with fine rays. Exam])lcs, pi. xvii. fig. 20 ; pi. xviii, fig. 

 13 ; pi. xix, fig. ■'). 



Plychopteria, Hall. Diflers from Actinopteria in the nasute anterior extrem- 

 ity, and large straight wing marked by a strong longitudinal fold. Hinge- 

 line narrow, linear ; furnished with one or two linear oblique cardinal and lateral 

 teeth. Surface with fine rays. Example, pi. xxiii, fig. 17. 



*.See note, pnge 81. 



