THE WEST AMERICAN MOLLUSKS OF THE GENUS AGAR 



By Paul Bartsch 



Curator, Division of Mollusks and Cenozo-ic Invertebrates, United States National 



Museum 



A recent inquiry by Prof. Joshua L. Baily, who is revising Keep's 

 " West Coast Shells," regarding the status of Area gradaia in Cali- 

 fornia made it necessary to subject the members of this group to a 

 critical examination; the results thereof are noted herein. The 

 change of concept here expressed is due in part to the splendid series 

 of specimens that we secured on the cruise of the United States Bu- 

 reau of Fisheries steamer Albatross in its explorations of the waters 

 of Lower California and the Gulf of California in 1911 and in part 

 to the contributions of many correspondents, both in the United 

 States and in the regions to the south, that have enriched the collec- 

 tion of the National Museum sufficiently to clear up some doubtful 

 problems. 



First of all, I believe that Acar, which was proposed by Dr. J. E. 

 Gray in 1857^ as a subdivision of the genus Barhatla, is entitled to 

 generic rank. The curiously elevated smooth muscle scars combined 

 with the peculiar shape and sculpture make it a compact unit group, 

 rather widely distributed in warm waters. 



Gray, in defining Acar (loc. cit.), mentions three species, namely, 

 Byssoarca reticulata^ B. divaricata^ and B. gradata, without designat- 

 ing a type. A type designation seems not to have been made until 

 1925, when Dr. Wendell P. Woodring ^ selected Area gradata 

 Broderip and Sowerby for that purpose. 



The genus Acar in the east Pacific ranges from southern Cali- 

 fornia to Peru, where it is represented by a number of species whose 

 distribution coincides quite well with the faunal areas as at present 

 conceived. 



1 Ann. Mag. Nat. Hist., ser. 2, vol. 19, p. 369, 1857. 



2 Miocene mollusks from Bowden, Jamaica, pt. 1, Carnegie Inst. Washington Publ. 

 no. 3GG, p. 36, 1925. 



No. 2909.— Proceedings, U. S. National Museum, Vol. 80, Art. 9. 

 70405—31 1 



