ABSTKACT OF THE CHARACTERS OF THE GENERA IN- 

 CLUDED IN THIS REPORT. 



For the sake of completeness and as a guide to the genera, it has 

 seemed expedient to supplement the specific descriptions by a short notice 

 of the generic characters with references to the accompanying plates. 

 These plates are intended to represent the characteristic generic forms, 

 and to convey in a measure some idea of the variety of forms embraced 

 in each genus. In a primary sense, the plates are also designed as a 

 key to the genera, and to facilitate the study of the principal charac- 

 ters of the monomuscular Devonian lamellibranchiata of the State of 

 New York. 



Pectbnidve 



Ptekiniid^e 



AviCULID^E 



• ine qui valve. 



Classification. 



Pernopecten. 



Crenipecten. 

 ( Aviculopecten. 

 Avipectenid^e 1 Lyriopecten. 

 ( Pterinopecten. 



Pterinea. 



s. g. Vertumnia. 

 1 Actinopteria. 

 [ Ptychopteria. 

 ' Limoptera. 



G-lyptodesma. 



Leiopteria. 



Leptodesma. 



Pteronites. 



Palseopirraa. 



Ectenodesma. 



Ambonychiidje •{ Byssopteria. ] 



f Mytilarca s. g. Pletliomytilus. I 



Mytilid^ 1 Mytilarca. ' equivalve. 



I Gosselettia. 

 { Modiola s. g. Mytilops. 



Pernopecten* Winchell. Shell like Pecten. Hinge with a central 

 cartilage pit and a crenulated hinge-plate on each side below the hinge- 

 margin. This and the following genus appear to be more nearly 

 related to the genus Pecten than to Aviculopecten. 



Examples — Pernopecten limiformis. PI. i, figs. 1, 2. 

 Pernopecten Shumardanus. PI. i, fig. 3. 



[Sen. Doc. No. 38.] 



* See note, page 277 



59 



