OUDKR T 



PRIONODESMACEA :u>7 



obsolete in the adult, t!i<>u<ih present in the young ; generally byssiferous ; hinge Schizodont 

 or edentulous. The young sometimes showing a distinct nepionic stage. Marine. 



Family 15. Pterineidae. Dull. 



Shell Pteriiform, bialate, dimyarian, the anterior adductor smaller ; inequivake, vet-y 

 inequilateral ; dentition obscure; ligament amphidetic, external, multivincular (?) ; the byssus 

 passing through a notch in tlo smulhr rnlve. Ordovician to Devonian. 



In Picrinca and its allies we have the first indications of divergence of what ultimately 

 became Taxodont and Schizodont dentition. From this assemblage, as indicated by ,J;u kx.n, 

 a large proportion of the Prionodesmacea have diverged in various directions. It is probable 

 that from this source the filibranchiate Taxodonts have sprung, rather than directly from the 

 ibliobranchs. 



Rhombopteria, Jackson (Fig. 617). Posterior wing separated from the body of the 

 valve by a shallow sinus ; anterior wing short ; teeth obscure, the posterior elongated. 

 Silurian. 



Pterinea, Goldf. (Fig. 618). Left valve convex, right valve flat ; hinge plate long, 

 broad, auriculate before and behind ; area amphidetic, grooved ; ligament parivin- 



I 



FIG. (517. 



/,Vm,,,/,, r /o-/</ mira, FIG. 61S. 



Han. sj>. Silurian (E); A, Pterinea laevis, Goldf. Devonian; Niederlahnstein, Nassau. Interior of left 



Prague(after Jackson). valve, i/i B, P- lineata, Goldf. Same locality; external view. 



cular (?) ; anterior teeth obscure, transverse ; the posterior elongate, nearly parallel to 

 the cardinal margin, depressed behind. Posterior adductor scar large, the anterior 

 small but strong, inserted below the anterior wing. Silurian to Carboniferous ; 

 particularly abundant in the Devonian of Europe and America. 



Actinodesma, Sandb. (Glyptodesma, Ectenodesma, Hall ; Dolichopteron, Maurer). Like 

 Pterinea, but with the wings elongated and pointed. Devonian. 



Leptodesma, Hall ; Kochia, Freeh (Onychia, Sandb. ; Loxopteria, Freeh). Devonian. 



Family 16. Lunulicardiidae. Fischer. 



Usually equivalve, triangular shells with terminal beaks, from which a sharp ridge 

 runs toward the lower margin, bounding a flattened area. Hinge margin straight, long. 

 Internal characters unknown. Silurian and Devonian. 



Lunulicardium, Miinst. Anterior side with a byssal sinus. Silurian and 

 Devonian. L. semistriatum, Miinst. 



Patrocardium, Fischer (Hemicardium, Barr. non Cuvier). Without byssal sinus. 

 Silurian. 



Additional genera : Amita (Spanila, Tetinka), Mila, Tenka, Babinka (Matercula\ 

 Barrande. Silurian. 



Family 17. Ambonychiidae. Miller. 



Shell Mytiliform, with no anterior wing, the anterior adductor obsolete; equivalve, 

 very inequilateral ; dentition obsolete or Schizodont ; ligament external, multivincular (?) ; 



