114 1-rilXoriHT' 



the whole breadth of South America between. That tlie Chalk-Direr 

 specimen is identical with the British Mu.-emn specimens is beyond 

 doubt. May not the difficulty lind solution in the fact that the "I. 

 of Plata," as it stands on ( 'inning's tablet in the British Museum, 

 and to which Sowerby (Joe. cit.) addt d "W. ( 'olumbia" is really some 

 island in the estuary of La Plata? 



The above criticism was iirst suggested to me by the Rev. K. 

 Boog Watson, to whom it gives me Lrreat pleasure to dedicate this 

 species. 



The single specimen in the collection is of a pink color mottled 

 with creamy yellow, with an obscure yellow line along the jugmu, 

 and with a pale spot on each side of the line on severed valves: 

 there are also several irregular dark patches; the posterior valve is 

 deep-rose below the umbo. The girdle is mottled brown and white, 

 there being a white patch sit the junction of each valve. 



The shell is long, narrow, and arched, anterior and posterior 

 valves with fine concentric ridges ; the umbo of the latter is prom- 

 inent. The intermediate valves are apparently smooth, but really 

 with extremely delicate longitudinal strire; the lateral areas are 

 characterized by wide ridges. The ligament has stout, tall, 

 imbricate scales. 



The three specimens of this species in the British Museum are 

 pink and only slightly flecked with white, no black or brown spots, 

 and in two of them the central areas have concentric lines like 

 those of the lateral areas. 



o. Qroup of I. pwictulatissimus. 



Small species, having the central and lateral areas closely and 

 minutely granulated. No riblets. West Indies and South Ameri- 

 can coasts. 



I. i-Ai-iLLOSUS C. B. Adams. PI. 21, figs. 40, 41. 



Shell small, oval, carinated on the back, the side slopes slightly 

 convex; surface not divided into distinct areas, apparently smooth, 

 but under a strong lens seen to be closely and evenly granulated 

 throughout; color whitish, closely mottled with olive-green; or 

 olive-green or olive-brown, with or without snow-white spots. 



The lateral an-a< are not raised, and are sculptured precisely like 

 the central areas, from which they are defined simply by an incon- 

 spicuous diagonal ridge. The posterior valve is moderately eleva- 

 ted, the umbo central, rather acute, posterior slope concave. 



