116 EOCENE MOLLUSCA. 



lanceolatd, bisulcatd ; ano ovato, obtuse circumdato, in medio prominenti ; apicibus depressis, 

 approximatis ; marginibus integris. 



Shell elongately ovate, smooth, thin, and slightly convex or tumid, inequilateral ; 

 pedal region ovately rounded ; siphonal region obliquely truncated, or very obtusely 

 rostrated ; lunule elongated with a central elevation or ridge ; anal region ovate and 

 centrally elevated ; beaks depressed j margins smooth. 



Length, 1 inch ; //eight, \ an inch. 



Localities. Barton {Edwards). 



This species has considerable affinity with N. bisulcata. It appears to differ in being 

 of a more elongated form, and in having the siphonal region more inflated ; the whole 

 shell appears to be more regularly convex, and the concentric lines or lines of growth are 

 more distinct than they are upon N. bisulcata. 



This shell, perhaps, was not covered with a very thick epidermis, as there are no 

 remains of if upon any of the specimens I have seen, and the beaks are not eroded. 



14. Nucula pr^elongata, S. Wood. Tab. XIX, fig. 1 a, b. 



Spec. Char. N. testa ovato-elongatd, pralongatd, tenui, lavigatd, convexiuscuM, 

 ineequilaterali ; pedi-regione ovato-rotundatd ; siphoni-regione brevi, subangulatd ; lunula 

 lanceolatd, bisulcatd; ano ovato, circumdato, in medio prominenti ; apicibus depressis, 

 approximatis ; marginibus crenulatis. 



Shell ovately elongate, thin, smooth, and slightly tumid, inquilateral ; pedal region 

 roundedly ovate ; siphonal side short and slightly angulated ; lunule elongate, with double 

 shallow depression ; corselet slightly prominent in the middle ; beaks depressed ; margins 

 crenulated. 



Longest diameter, 1 inch nearly. 

 Localitg. Bracklesham {Edwards). 



Only two or three specimens of this species have come under my observation ; they 

 somewhat resemble in form N. pralonga, but the crenulated margin will distinguish them, 

 and there is a difference, also, in their comparative lengths. This shell seems, also, to be 

 more iridescent than N. pralonga, and rather more deep or tumid. 



Two other specimens from the same locality, in Mr. Edwards's cabinet, have a somewhat 

 similar outline, but they have not the basal portion of the anal region quite so much 

 extended or angular; they appear, also, to have a more distinct lunule and corselet than 

 the one figured {pralongata) ; and these depressions (lunule and corselet) are divided by 

 a small central ridge, which I do not perceive in our figured specimens. I am, however, 

 unwilling to separate them, as they otherwise correspond, and future observations must 

 determine whether they be the same or different. 



