H 



JOHAN KIÆR. 



M.-X. Kl. 



The interior of the ventral valve has its greatest depth near 

 the centre, and on both sides of the base of the pedicel tube exhibits a 

 deep impression I text-fig. 3 1, that appears as a strongl}- marked dentate 

 process in the casts of the shell. This process is probably the marking ot 

 the transmedial and lateral muscles!?). In addition, we see as a rule a more 

 or less clear impression of the central viscelar area, from which the two 

 vascular sinuses emerge to the sides. The}' usually- run in a sharp curve 

 parallel to the outer edge of the shell (fig. 4 — 5) and less frequently are 

 directed more foreward (fig. 91. As a rule we see only the posterior 

 portion of these curved impressions clearly. At the inner portion, between 

 the viscelar area and the vascular sinu, we sometimes see two small round 

 muscle-like impressions. 



The interior of the dorsal valve has its greatest depth near 

 the posterior edge. Just in front of the area we sometimes find two con- 

 vergent, faint, dentate processes. Within these, on each side, there are 

 almost always two more or less distinct and almost coherent impressions 

 of muscles — presumabl}' of the lateral muscles (pi. I, fig. 6 — 8 and text- 

 fig. 3). In the middle of the shell we sometimes see a faint, raised portion 

 — usually indistinct — that separates into two divergent branches in front. 

 When preserved, this forms a characteristic figure that reminds one of the 

 two thighs of a frog; at its sides, to the rear, we sometimes find two small 

 muscle-like impressions. 



The marginal border of the shell as a rule is narrow, but varying. 



Dimensions: The length of the shell seldom exceeds 7 mm.; the 

 breadth is somewhat greater; reference is made to the following table: 



No. 



Length 



Breadth 



