202 Nelson on Tertiary MoUiisca of Peru. 



mis, and marked by broad, flat, concentric ribs, which become larger 

 and smoother over the middle of the shell, but not wholly obsolete. 

 With the epidermis removed the shell still shows the striations, 

 especially about the beaks. Hinge line nearly straight, very broad. 

 The median tooth (cardinal) of the right valve is large and pointed ; 

 posterior cardinal deeply bifid. Lateral tooth large, nearly as long 

 as the posterior cardinal, and parallel with it. In the left valve the 

 median cardinal is bifid throughout the upj^er half of its length. 

 Hinge area forming a very obtuse angle with the ligament area. 

 Muscular scars and palial impression not observed. A young and a 

 full grown specimen give the following measurements : 



mm 



Young, Length, 4G-05mm Breadth, 47-lnim Height, 22-6 



Mature, " 95-60 " 952 " 47 2 



This is the most common bivalve in the collection. The species is 

 peculiar in that the young specimens are proportionally wider than 

 long, while full grown specimens are slightly longer than wide. The 

 species most nearly resembles D. ponderosa Gray, but is much thicker 

 and stouter, more elongated, and has the sulcations more distinct. 

 D. grandis is much larger, also, than I). Dunkeri Phil., and more 

 elongated, and the ribs are coarser and flatter. 



Chione variabilis, sp. nov. 



A very variable species, somewhat resembling Chione g7udia 

 Brod. and Sby., and also allied to Chione amathusia Sby. The 

 " concentric frills " are not preserved, but the position of the scars 

 which they have left, and the ai'rangement of the radiating ribs, 

 show the species closely allied to Chione gnidia. 



It difiers from that species in having the central tooth of the hinge 

 line more strongly furcate ; in having the ligament scar less deeply 

 impressed and the lunule broader. The shell is also proportionally 

 longer and the posterior margin shorter. The crenulations of the 

 hinge margin resemble Chione gnidia.^ while the teeth more closely 

 resemble C. amathusia ; the cardinals are, however, more divergent 

 and apparently more rounded on the summit. Measurements as fol- 

 lows: length 28-42 millim. ; breadth 30 millim. ; 2d, length 28-85 mil- 

 lim. ; height 19-9 millim. 



Specimens having a length of 50 to 60 millim. occur, but not per- 

 fect enough for measurement. 



Chione, sp. ind., A. 



With the preceding species there was fotxnd a fragment of a right- 

 valve, which differs in having the lunule very elongated and the um- 

 bos not reaching to the margin. 



