PALEONTOLOGY ZORRITOS FORMATION 171 



The only discrepancy in the transition lies in the unusual 

 size of C. bradleyi, which is 20 mm. long and 18.5 mm. high; 

 the largest of the other species is 10 mm. in length. Pro- 

 portionally considered, however, the external characters of 

 the species grade into one another, with sufficient difference 

 between each and its neighbor in the series to require system- 

 atic distinction. 



Corbula (Aloidis) bradleyi Nelson 



PLATE X Figs. 13, 14. 

 Corbula bradleyi Nelson, Trans. Conn. Acad., vol. 2, p. 200, 1870. 



"Shell very ventricose; wedge-shaped, umbones large, 

 convex, incurved over the hinge area. Anterior margin 

 rounded ; lunule very deeply impressed ; ligament area twice 

 the length of the lunule; strongly angulated with the poste- 

 rior margin. Hinge tooth large, recurved ; fossette triangular 

 and deeply impressed. Surface of shell marked by strong, 

 convex, concentric lines, separated by narrow but well 

 marked spaces, about five of the lines in five millimetres. 

 The triangular shape is very characteristic, as is also the 

 angulation of the posterior margin ; beak very prominent." 

 Nelson, 1870. 



The posterior surface is marked by two carinas about 5 

 mm. apart at the hinge, between which the surface is flat 

 to somewhat excavated. The strong lirae curve across this 

 surface, diminishing in size as they converge across the im- 

 pressed area which Nelson has incorrectly described as an 

 escutcheon. The liration tends to be irregular ventrally. 

 Length, 20; height, 18.5 mm. 



Unfortunately, Nelson's collection affords but one right 

 valve of Corbula bradleyi, and it does not occur in the Hop- 

 kins collection. Relationships which might hinge on char- 

 acters of the left valve are accordingly impossible of note. 

 However, the characters offered by the specimen available 

 show that, other things being equal, C. bradleyi has a defin- 

 ite place among the Miocene members of the section Aloidis. 



