406d Thirty-fifth Eeport oisr the State Museum. 



Pteronites, McCoy. This genus is restricted to those possessing the 

 characters of the original types. Body very oblique. Hinge-line 

 longer than the body of the shell. Wing and hinge extended poste- 

 riorly. Test marked by concentric striae. 



Example — Pteronites profundus. PI. iv, fig. 17. 



Palceopinna, Hall. Shell, in outline, somewhat similar to Pinna, 

 gaping in front. Test marked by fine radiating lines. Body more 

 convex and test with finer rays than in the ordinary Pinna. Hinge- 

 line simple. 



Example — Palceopinna Jldbella. PI. v, fig. 14. 



JEctenodesma, Hall. Resembles G-lyptodesma in outline, except that 

 the anterior wing is more produced and both wings more acute at their 

 extremities. Test ornamented with rays. 



Example — Ectenodesma birostratum. PI. hi, fig. 8 ; PI. iv, fig. 18. 



Byssopteria. Shell erect, equi valve. Alate posteriorly, truncate, 

 and with a nasute projection in front. Surface radiated. 



Example — Byssopteria radiata. PI. v, fig. 13. 



Mytilarca, s. g. Plethomytilus, Hall. Equivalve, mytiloid, gibbous 

 shells with a finely striated ligamental area. Posterior side subalate. 

 Hinge-line transverse. Lateral teeth small, oblique ; no cardinal teeth 

 have been observed. Test with concentric striae. 



Examples — Mytilarca (Plethomytilus) ponder osa. PI. v, figs. 1, 2. 

 Mytilarca (Plethomytilus) oviformis. PI. v, fig. 4. 



Mytilarca, Hall. Shell equivalve, inequilateral and mytiliform with 

 terminal beaks and short hinge-line, which is bordered by a flattened, 

 longitudinally striated, ligamental area of greater or less extent. Car- 

 dinal teeth small, situated beneath the beak. Posterior teeth small 

 and oblique, situated at the post-cardinal extremity of the hinge. Test 

 free from radii, with a single known exception. 



Examples — Mytilarca lata. PI. v, fig. 3. 



Mytilarca Ghemungensis, PI. v, figs. 5, 6. 

 Mytilarca carinatu. PI. v, figs. 7, 8. 



Gosselettia, Parrots. Shell subtriangular, truncate on the anterior 

 side, subalate on the posterior side. Ligamental area wide, longitudi- 

 nally striate. Cardinal teeth strong, situated under the beak. Lateral 

 teeth elongate. Surface marked by concentric striae. 



Example — Gosselettia triquetra. PI. v, figs. 9, 10. 



Modiola, s. g. Mytilops, Hall. The fossils of this genus resemble 

 Modiola and Lithodomus in external form, and may also be compared 

 with the fossil genus Myoconcha. Hinge-line narrow, oblique, ex- 

 tending about one-half the length of the shell. Beaks terminal. 



Example — Modiola, (Mytilovs) prcecedejis. PI. v, fig Si n r 12. 



