328 PROCEEDINGS OF THE ACADEMY OF [DcC, 



the average larger than sandvichensis; there is rarely any trace of 

 corrugation, and the beaks are often very long. This form may 

 prove to be a distinct species when perfect specimens come to hand. 

 It may temporarily be called 0. sandvichensis margaritce (PI. 21, 



fig. 9). 



According to Bryan, the native name of this oyster is pioeoe. It is 

 too small to be of econonic value. 



Ostrea hanleyana Sowerby. PI. XXI, fig, l. 



1871. Ostrea hanleyana Sowerby, Conch. Icon. Vol. 18, Pi. 28, fig. 72 

 (Sandwich Islands). 



Oahu-: Mokuoloe Island, Kaneohe Bay (Kuhns and Thaanum) ; 

 Mokapu Point; Paumalu (Bryan), Molokai: Kainalu (Bryan). 

 Hawaii: Hilo (Thaanum). 



This is a rounded or oval oyster, usually showing slight traces of 

 fluting, or in others this is scarcely noticeable, creamy white outside, 

 white within, or having vinaceous stains. The attached valve 

 generally projects broadly beyond the other. The adductor scar 

 is small, shortly oval. There is some minute crenulation of the 

 inner edges near the beaks, which are alwaj's very short. The 

 usual length is 35 to 60 mm. 



Ostrea retusa ' Pease' Sowb. P!. XXI, fig.s. 2, 3. 



1871. Ostrea retusa Pease, Sowerby, Conch. Icon. Vol. 18, PL 19, fig. 42 



(Sandwich Is.). 

 1916. Ostrea retusa Pse., Bryan, Natural History of Hawaii, p. 115 (Pearl 



Harbor, fossil). 



Pearl Harbor, Oahu (Bryan, Kuhns, Pilsbry). 



This oyster has not yet been found living, the specimens being 

 from deposits believed to be pleistocene, on the shores of Pearl 

 Harbor. I found it in abundance in a railroad cut about one-fourth 

 mile east of Waipio, where a section of the ancient oyster bed is 

 exposed. 



It has been taken by Prof, and Mrs. Bryan at Waipahu, and by 

 Kuhns and Bryan on the southern border of Ford's Island. 



The extinction of the species may have been due to an inflow of 

 hot water from one of the tufa cones northward, as Prof. Bryan 

 suggests to me; or possibly a heavy fall of volcanic ash was blown 

 over Pearl Harbor, and the shell fish were smothered by the turbid 

 water. At all events, the species has not been found elsewhere in 

 the islands, either recent or fossil. We may infer that it had been 

 remarkably restricted in distribution for sometime previous to its 

 extinction. 



It is always a long, narrow oyster. The lower valve is frequently 



