128 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Geographic distribution same as Haroldiana. 



G. angidata, angulata Uaroldiana, and angulata suhangulala all occupv 

 or occupied the same geographic range. Angulata is confined to rapid 

 streams and rivers with considerable current; Haroldiana to sloughs, 

 sluggish creeks, and slow-moving rivers ; while subangulata was an 

 abundant ]S'aiad in the great lakes which existed on the Pacific Coast 

 during the Pliocene period, a situation in wliich angulata is never and 

 Haroldiana seldom found. This is an excellent instance of a change 

 of station accompanying the evolution of the shell, and therefore of 

 particular interest. 



In attempting to classify this species genetically the writer has 

 been in somewhat of a quandary. Either two comprehensive stages 

 equivalent and analogous to sub-genera in all the other Unionidae 

 must be treated as one sub-genus (necessitating a definition sufficiently 

 broad to cover half the family and several genera which have nothing 

 to do with this series), or the species must be arbitrarily divided 

 into two species simply because the extremes are sufficiently distinct, 

 without regard for an unbroken chain of intermediate stages, or one 

 sub-species must be placed in one sub-genus and two in the other. 

 The last alternative has been followed, since it is most nearly in 

 keeping with natural relationships in the ]Sraiades, though the writer 

 does not regard it as desirable from a classification standpoint. It is 

 an unfortunate limitation of the Linnean System that no disposition 

 was made in case intermediate forms have not died out, or died out 

 but left fossil remains. 



The young of this species have been found in deep quiet reaches of 

 water burrowing into stiff mud or clay ; juvenile Haroldiana occur 

 in similar situations. 



GoxiDEA Hemphilli, u.sp. PI. YII, Fig. 19. 



Shell reminding in a general way of G. angulata Haroldiana, but 

 decidedly smaller, proportionally more elongate, the postero-ventral 

 ridge less sharply defined and terminating in a rounded margin, shell 

 not broader posteriorly, and less obliquely decurtate behind, hinge 

 with a very rudimentary pseudo-cardinal in each valve ; habitat 

 apparently lacustrine. 



Length 31, breadth 14, depth of valve 5 mm. 



Miocene : Contra Costa Lake beds, California. 



Water-tunnel, head of Telegraph Caiion, Berkeley Hills, California. 



Named after Mr. Henry Hemphill, the veteran collector. 



Genus Aexoldixa, n.gen. 

 Anodonta (sp.), Lewis, 1875 (A. dejecta, Lewis). 



Type, Ajiodonta dejecta, Lewis. 



Shell of rather large size, averaging 80 mm. in length, anodontiform, 

 sub-solid, elongate-elliptical, distinctly broader posteriorly, moderately 

 inflated, beaks which are not elevated above general curvature of 

 shell, marked by prominent calycules and a few coarse doubly looped 

 ridges alternating with pits which lie along the postero-ventral ridge, 



