Vol. 4] 



Osmont. — Areas of California Neocene. 



99 



ah oa CANAbis Conrad. 

 Plate ]], Figs. 7, 7 a and 7b. 



Arm Can, ills Conrad. Pac. K. R. Reps., 1854-5, Vol. 6, p. 70, PI. 2, 

 fig. 8. 



Description. — This species was described by Conrad as fol- 

 lows: ' ' Subtrapezoidal, ventricose, ribs 24-26, flattened, scarcely 

 prominent, divided by a longitudinal furrow, disk concentrically 

 wrinkled, umbo ventricose, siinnniis prominent, remote from the 

 center." 



There seems to be little difference between this form and 

 .1. trilineata, the principal difference being that the beaks are 

 more distant and less incurved and the ligament area in .1. ca- 

 nalis more flaring. The additional grooves, and also the beaded 

 effect of .1. trilineata, seem to appear occasionally on A. canalis 

 also. The flare of the ligament area does no1 appear to be an 

 absolutely constant factor, and ils importance as a specific char- 

 acter is somewhat doubtful. 



Occurrence <in<l Associated Fauna. — This species occurs at 

 Santa Barbara, as noted by Conrad, and is called Pliocene by 

 him. Specimens are also known from the McKittrick Oil Dis- 

 trict, from a horizon very doubtfully referred to the San Pablo. 

 It is cited by Ashley as occurring in the Half Moon Bay and the 

 Capitola sections. The writer has seen specimens from Half 

 Moon Bay. It seems therefore to be a form closely related to, 

 if not identical with. .1. trilineata Conr., and to have the same 

 range as that species. It also occurs in the San Pablo of Zapato 

 Chino Creek, Fresno County, the fauna of which is listed under 

 A. trilineata. 



CONCLUSIONS. 



The above species comprise all the Neocene areas of Cali- 

 fornia, so far as the writer has been able to determine. Other 

 species are mentioned by Conrad, viz. : A. congesta and A. obis- 

 poana. The figure of the latter is very poor. It may represent 

 A. montereyana, but is not perfect enough for identification 

 More investigation may, however, show it to be a valid species. 

 The former might be the young of any one of several species. 



As to vertical range, we may, from our present knowledge, 

 fairly assume that : 



