120 University of California Publications in Geology [Vol.11 



A. muta resembles A. castrensis Hinds, 87 , a Recent West Coast 

 species, from which it differs in the following respects : It is somewhat 

 higher in proportion to the length, the anterior end is broader and 

 the ribbing is somewhat finer. The escutcheonal area is more sharply 

 defined on the former than on the latter. 



The escutcheon of A. muta is very similar to that of A. shumardi 

 Dall ; the two species differ, however, in sculpturing and in outline ; 

 the latter is decidedly the longer, the ventral edge being less arcuate, 

 and the pouting of the escutcheon more prominent ; also, the cardinals 

 are more numerous. 



The writer feels certain that this species has been determined in 

 several recent faunal lists as A. conradi Meek, as redescribed by 

 Dall. 88 The form figured by him as A. conradi Meek came from the 

 Empire beds of Coos Bay, Oregon (Pliocene). The sculpturing on 

 A. muta is coarser than that on this Pliocene species, and there is a 

 distinct escutcheon on the former which is not seen on the latter. 



In the Lower Miocene sandstones, immediately above the Oligocene 

 shale, at the town of Astoria, Oregon, there is a third species of Acila 

 which is distinct from both A. muta and A. conradi as redescribed by 

 Dall. This form is very possibly the true A. conradi. 89 The writer 

 has not seen the type of A. conradi, but the figure of Conrad's Acila 

 divaricata, which is the type of A. conradi, is poor and his description 

 meagre; for this reason, for the present, the name A. conradi (as 

 redescribed by Dall) is retained for the Pliocene species. The writer 

 has never seen this species, which is found in the Pliocene of Oregon, 

 in any collections from either the Lower Miocene or Oligocene. 



8? For original description of A. castrensis, see Hinds, R. B., Zool. Voyage 

 "Sulphur," p. 61, pi. 17, fig. 5, 1844. 



ss Dall, W. H., IT. S. Geol. Surv., Prof, paper no. 59, p. 102, pi. 12, figs. 4-5, 

 1909. 



89 The writer has had access to two fairly large collections from the Oligocene 

 and Lower Miocene from the vicinity of the town of Astoria, Oregon. One of 

 the collections is in the California Academy of Sciences, the other at the Univer- 

 sity of California ; the latter collection was made by Ralph Arnold and Harold 

 Hannibal, the former by F. M. Anderson and Bruce Martin. 



Acila conradi (Meek) was first described and figured by T. A. Conrad as 

 Nucula divaricata (Amer. Jour. ScL, vol. 5, p. 432, fig. 1, 1848) ; later it was 

 found that this name was preoccupied and in a check list by F. B. Meek ; the name 

 w x as accordingly changed to Nucula conradi. (Check list Miocene Fossils N. Am., 

 Smithson. Misc. Coll., vol. 7, no. 183, p. 27, Nov., 1864; also, Conrad, Am. Jour. 

 Conch., vol. 1, p. 153, 1865.) 



