NATURAL SCIENCES OP PHILADELPHIA. 145 



Unio Danai. 



Shell elongate, arcuate, and oblique, contracting posteriorly ; anterior end 

 regularly rounded; base slightly arched, most contracted a liltle behind the 

 middle ; posterior end cuneate, rather narrowly rounded ; dorsal margin slop- 

 ing with a long convex curve from near the umbones towards the posterior 

 end ; beaks depressed, not very distinct from the dorsal edge, placed a little more 

 than one-fourth tlie length of the shell from the anterior end; flanks concave 

 from the umbonial region obliquely downwards to the most arcuate portion of 

 the base ; liinge moderately thick; cardinal teeth corrugated, strong, apparently 

 double in the left valve, and single in the right; lateral teeth long and slender : 

 surface (of specimens with the epidermis removed) marked by faint lines of 

 growth, and very obscure radiating stria;. Length 3-50 inches ; height 1'54 

 inches; breadth about 1 inch. 



After satisfying ourselves that this and the two following species are distinct 

 from all the fossil Uniones described in any works within our reach, we sub- 

 mitted them to Mr. Isaac Lea, tlie well-known conchologist of Philadelphia, from 

 whom we received the following remarks respecting their affinities to recent 

 species. 



" The specimen marked Unio Danai has very much the same outline with 

 Margarilina margaritifera^ Schm., but is a true Unio, and perhaps more nearly 

 allied to U. lumidus, Retzius, than to any other of the genus. It is certainly an 

 undescribed species. 



" Unio Deiceyanus is a very distinct species, and although not more than half 

 the size, very closely resembles the recent U. ^rwwca^Ms, Swainson, in outline and 

 obliqueness. It is also, like it, a thick ponderous species. 



" Unio subspalulaius is an oblique species, nearly allied to U. spatulalus, Lea. 

 but is more rounded posteriorly than that shell. 



" All these species are characterized by an obliqueness not usual in the genus. 

 The beaks are nearly terminal in all of them, and they have a general massive 

 character, which causes a disposition to enlarged cardinal and lateral teeth. 

 This enlargement is more particularly noticeable in the cardinal teeth, which 

 are all massive and very much corrugated. It is evident from the deep cor- 

 rugations of the great cicatrices, that the muscular power of the animal was 

 very great. 



" They are certainly very interesting specimens, and deserve attention, as they 

 differ much from the general type of recent Uniones, as well as those of tlie 

 Wealden of England." 



Owing to the fact that these shells were obtained from a formation in which 

 saurian remains, similar to some of those of the Wealden were found, we 

 called Mr. Lea's attention to that fact, with the view of also obtaining his 

 opinion respecting their affinities to Wealden forms. From his remarks above, 

 it will be seen he is of the opinion they are distinct from the types of that epoch. 

 Mr. Lea's opinion on this point is of much value, since he had an opportunity, 

 while in England some years since, of studying very carefully Dr. ManteU's ex- 

 tensive collection of Wealden species. 



We name this shell in honor of Prof. James D. Dana, the distinguished 

 naturalist of New Haven, Connecticut. 



Localitji and posilion. Mouth of Judith River, bed G. of the freshwater and 

 estuary deposits at that locality. 



Unio Deweyanus. 



Shell rather thick, oblique, narrow-ovate, approaching a narrow-elliptic 

 form, most convex in the umbonial region, more compressed and cuneate poste- 

 riorly; extremities rounded, anterior end a little wider than the otiier ; base 

 broad, semi-ovate ; dorsal margin nearly straight, and sloping gradually from 

 near the beaks towards the posterior end ; beaks small, not very distinct from 

 the dorsal border, almost terminal in old shells, but iu young individuals a 



1857.] 



