- 204 - 



ing Dall's varietal nanie to ST:eeific rsnlc. The outline of the 

 shell is soraev/hat variable, some of the shells being more orbi- 

 ciilar than the tyi-^ical slightly elongate form. On some valves 

 the anterior submarrin is narrower than the posterior and is with- 

 out radial sciilpture, while on the posterior one radial sculpture 

 ma^" or may not be present. Tn general, this species is charac- 

 terized by its small, thin shell, suborbicular and moderately in- 

 flated outline and nujnerous, finely sculptured ribs. Immature 

 right valves are especially conspicuous because of their compress- 

 ion and unusually long anterior auricles. The few inriividiials with 

 rounde" ribs ajid slightly scabrous anterior anrl posterior rib£> dif- 

 fer from the yomag of the asso:7ia.ter" p. ( AequiTjecten ) sumpleus 

 n. sp. of the same size by having more numerous and more slender 

 ribs, narrower interspaces, with at no tire all the ribs scabrous. 



Toula's figure reproduces an incom.plete right valve v^'hich 

 agrees, as far as the figure is concerned, v/ith vaginulus . He 

 notes, however, that the ribs display a tendency to berjome f^icho- 

 tomous on the middle of the disk. Since his material furnished 

 only two fragmentary valves it is difficult to determine whether 

 his form is icientical. 



Occiirrer.ee .- Upper Oligocene : ? Gatun, Panama (To^ila, 1908), 

 Lower Miocene: 3owden he's, Bowden, Jamaica, (Dall, 1898). 



