116 THE NAUTILUS. 



during the eighty-four years which have elapsed since Sowerby 

 characterized the genus, only one more recent species which can 

 confidently be affirmed to belong to the typical section of the genus 

 has been described. This is the P. loreni Jeffreys, 1881. P. Can- 

 dida has its hinge composed of a pair of nymphs sustaining the 

 external ligament, and in front of the nymphs a triangular area, 

 directly under the beaks, wiiich supported an internal resilium, some 

 fibers of which still adhere to the specimen in the National Museum. 

 The anterior edge of the resiliifer is raised into a rib-like prominence, 

 which is what in descriptions of the genus is usually referred to as 

 an "obscure tooth." It is not a tooth, but a reinforcement of the 

 pit or chondrophore. Not having a specimen for study in 1895, my 

 description of this hinge from figures (Trans. Wagner Inst., iii, p. 

 530) is to this extent inaccurate. It is true that Verrill in 1881, 

 and Locard in 1898, have described two bivalves under the names 

 of Pholadoniya arata and P. africana (Fischer MS.), but these do 

 not belong to the typical section of the group and may belong in a 

 wholly distinct genus. They are wedge-shaped, truncate shells with 

 the chondrophore obsolete, and having an aspect which leads one to 

 doubt whether the resilium was developed at all in either of them. 

 Their soft parts are wholly unknown. It is therefore a matter of 

 especial interest that in recent work of the U. S. S. Albatross in the 

 N. W. Pacific, Aug. 10, 190G, at station 4904, in 107 fathoms, a 

 right valve of Plioladumya was obtained, v.hich I now propose to 

 describe. 



Pholadomya pacifica n. sp. 



Shell resembling an unusually plump specimen of Mya arenaria 

 in general form, white, very thin, the beaks near the anterior third; 

 inner layer of the shell pearly; beaks low, slightly prosocoelous; 

 anterior margin of the valve evenly rounded, posterior a little 

 attenuated and with a slight gape but also rounrled; hinge-line thin 

 with a short, narrow nymph, the chondrophore also narrow, directed 

 obliquely backward, under and nearly parallel with the nymph; 

 interior polished when fresh, the S|)ecimen rather dull, almost con- 

 cealing the pallial sinus, which is less deep than in P. Candida. The 

 muscular impressions are obscure, but seem to agree with those of 

 hat species; exterior largely, finely granulose, like many Thracias, 

 sculptured with more or less evident lines of growth, and with abo 



