734 



AETHROPODA 



PHYLUM VII 



Family 1. Lininadiidae Baird. 

 Family characters the same as above given for the order. 



Estheria Eiijipel (Figs. 1417, 1418). 

 united by a straight tootliless margin. 



Shell composed of two thin rounded valves, 

 External surface concentrically ridged or 



Fig. 1417. 



Estheria minuta Alberti. Lettenkohle Dolo- 

 mite ; Sinsheim, Baden. A, i/j. B, 6/j. C, 

 Portion of the exterior, 50/j. 



FlO. 141S. 



Estheria sp. indet. Lower barren 

 Coal Measures ; CarroUton, Oliio. 

 Umbonal portion showing muscular 

 or nuclear node, i3/j. 



striated, and between the ridges are more or less regularly interlacing or branching 

 striae. The latter character serves to distinguish this genus from Posidonomya among 

 Pelecypods. The beaks are not sharply defined, and the primitive portions sometimes 



bear a strong ocular or muscular node. 



The genus Estheria has numerous fossil representatives, being first met with in the 

 Devonian, and occurring mostly in brackish and shore deposits. It abounds in the 

 productive Coal Measures, in the Permian, Trias (Lettenkohlenmergel) and 'W^ealden, 

 and has been found in the Pleistocene clays of Canada. 



Leaia Jones (Fig. 1419). CarajDace marked by one or two diagonal ridges 



Fio. 1419. ■ 



A, Leaia teidyi Jones. Coal Measures ; Potts vi He, 

 Pennsylvania. B, Lcdia haentschiana Geinitz. Coal 

 Measures ; Neunkirclien, near Saarbriicken (after 

 Golden berg). 



Fig. 1420. 



Schizodiscus capsa Clarke. 

 Hamilton ; Centerfleld, New 

 York. 2/j. 



which run from the anterior end of tlie dorsal margin toward the lower margin. 

 Carboniferous ; Europe and North America. 



EstherieUa Weiss. Carapace as in Estheria, but with radial riblets crossing the 

 concentric striae. Permian ; Russia. Buntersandstein ; Saxony. 



Schizodiscus Clarke (Fig. 1420), Carapace peltate, with a straight hinge which 

 is in the major axis of the shield. Each valve nearly a semicircle ; surface marked 

 with concentric ridges. Middle Devonian ; New York. 



Lepeditta Matthew. Cambrian ; North America. 



