90 • SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.53 



the interior of the dorsal valve the cardinal scars are very large and 

 extend forward nearly one-third the length of the valve. 



Type. — Acrothele granulata Linnarsson [1876, p. 24]. 



I w^as at first inclined to place this form under Botsfordia, but the 

 advanced position of the apex and pedicle opening of the ventral 

 valve indicates a closer affiliation with Acrothele. The short lis- 

 trium of Botsfordia has developed in Redlichella to the strong false 

 area of Acrothele, but the visceral area and main vascular sinuses of 

 Botsfordia remain practically unchanged. I regard Redlichella as 

 a form intermediate in development between Botsfordia and Acro- 

 thele. 



Genus LINNARSSONELLA Walcott [1902, p. 601] 

 LINNARSSONELLA MODESTA, new species 



Plate 9, Figures 8 and 8a 



Shell minute; general form subcircular. Ventral valve moder- 

 ately convex ; beak small and slightly incurved over a very low false 

 area; foraminal opening minute exteriorly, with a slightly elevated, 

 sharp ridge on each side a little in advance of the point of the beak ; 

 seen from the back, the minute aperture points backward from the 

 bottom of a pit between the two short, sharp ridges. In a specimen 

 from a layer of limestone a short distance above in the section the 

 aperture is at the point of a small nipple-like projection, apparently 

 formed by the union of the ends of the ridges, already described, on 

 each side of the aperture. Dorsal valve slightly convex, with a 

 minute beak at the posterior margin. 



Surface dull when the outer layer of the shell is preserved ; it is 

 marked by a few very fine, concentric lines of growth. The inner 

 surface is marked by concentric lines and a few fine, radiating lines. 

 The shell is formed of several layers or lamellae and is relatively 

 thin. 



The average diameter of the adult shell is from 1.75 to 2.25 mm. ; 

 the dorsal valve is slightly shorter than the ventral. 



The cast of the interior of the ventral valve shows a slight longi- 

 tudinal median elevation and two short, not very strongly marked 

 main vascular sinuses; several specimens indicate a slight cavity just 

 beneath the aperture which probably represents the inner side of the 

 foraminal tube. The interior of a dorsal valve shows main vascular 

 sinuses quite close to the outer margin ; also two small, rounded 

 median depressions a short distance in front of the posterior margin. 



Observations. — This shell occurs in great abundance on the sur- 

 face of shaly gray limestone about midway of the strata referred to 



