602 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxv. 



sandy shales and thin-bedded sandstones, also in arg-illaceous shales 

 above the Knox sandstone. 



Failing to establish a satisfactory genus in honor of Dr. Liiniarsson 

 in the first instance. I make another attempt with this rare and inter- 

 esting form. 



LINNARSSONELLA GIRTYI, new species. 



Shell minute. General form broad ovate to subcircular. Ventral 

 (pedicle) valve convex; beak small and slightly incurved over the false 

 area; false area short and varying from vertical to a backward inclina- 

 tion of 45^ to 50^ with the plane of the edge of the valve. In some 

 examples the margin of the false area arches, while in others it appears 

 to be straight. A very slightly indicated pseudodeltidium occurs 

 beneath the beak, that gradually widens to the margin, very much as 

 in Iphidea ■pealeL Foraminal opening minute exteriorly, but the tube 

 increases in size toward the inner surface of the shell. In one very 

 perfect shell the aperture appears to open into a narrow elongate 

 depression just in front of the ))eak, but it usually is seen as a minute 

 circular perforation in front of the beak. Dorsal (brachial) valve 

 gently convex, with a minute beak at the posterior margin. Surface 

 of the shell glossy and smooth to the unaided eye. but a strong mag- 

 nifier shows very tine concentric strife and lines of growth. The inner 

 surface is marked outside of the visceral area by very tine radiating 

 striw. The shell is formed of several lavers or lamella?, and, judging 

 from the depth of the impressions of the muscle scars and vascular 

 markings, is rather thick over the central and posterior portions. The 

 average length of the ventral valve is 1..5 to 1.75 nun. The dorsal 

 valve is slightly shorter. 



The cast of the interior of the pedicle valve shows the presence of a 

 large cardinal scar on each side of the visceral area and outside of the 

 YQvy strong vascular canal; they are oval in outline and probably the 

 point of attachment of strong muscle or muscles. The visceral area 

 is small, but is well defined. Of the vascular canals, only the main 

 trunks are shown by strong ridges in the casts: in one specimen they 

 extend almost in a direct line from the beak to the antero-lateral mar- 

 gins of the valve. The cast of the interior of the foramen is usually 

 broken ofi*. The interior of the brachial valve is beautif ull}' shown by 

 one specimen; the narrow area with its well-defined pseudodeltidium, 

 the large oval cardinal scars immediatel}' in front of the area, and the 

 strong vascular canals are as clearh^ defined as in the large shells of 

 Ohohis. The cardinal scars are divided into three parts b}" two trans- 

 verse lines crossing the outer slope more or less obliquely, but the 

 divisions on the two sides are unequal; the inner slopes of the scars 

 are finely polished and afford no evidence of the attachment of muscles. 

 Traces of the central scars occur on the outer slope of the cast of a 



