20 OLAF HOLTEDAHL. [SEC. ARCT. EXP. FRAM 



Strophonella HALL. 



Strophonella cf. euglypha His. 



PL VII, fig. 4. 



The fragmentary exterior side of one ventral valve and the hadly 

 preserved interior side of another are all that can be seen. The specimens 

 are comparatively small, measuring in width only 2 cm. The outline is 

 subtriangular, the posterior half of the valve slightly convex, the valve 

 at about the middle of the length curving concavely, with an angle of 

 about 130. On the surface a system of relatively very faint radiating 

 striae of first order, between any two of which are from two to five finer 

 ones. The distance between any two of the stronger ribs and also the 

 number of finer ones between them is greater in the posterior than in 

 the anterior part, as a rapid interpolation of new strong ribs takes place 

 towards the anterior margin. 



The specimen showing the interior is too much worn to show the 

 exact form of the muscular scars, only the strongly curved outer ridges 

 are indicated. 



This species looks very much like the common European Silurian 

 Strophonella euglypha His., but is smaller and has a less marked 

 striation than typical specimens of this form. In general form the 

 specimens also approach small types of Strophonella leavenworthana 

 HALL from the Lower Helderberg of New York but differ in the sur- 

 face ornamentation. 



Occurrence: B, lower part, Reindeer Valley. 



Orthothetinae. 



Schuchertella GIRTY. 



Schuchertella interstriata HALL. var. sinuata nov. var. 



PI. VII, fig. 6. 



Only one good, nearly complete specimen to hand. The outline is 

 subrectangular as the lateral margins only very slightly diverge anteri- 

 orly. The length of the hinge-line is accordingly very slightly shorter 

 than the greatest width of the shell. The ventral valve is nearly flat, 

 with a very slight elevation of the beak region, especially the portion just 

 in front of the beak itself and an up-curvature of the margins on both 

 sides of the centre of the front, in other words, we have a sinual 

 depression at and near the anterior margin. The dorsal valve regularly 

 convex but not markedly so. The low smooth triangular area of the 

 ventral valve with its convex deltidium is easily discerned, no dorsal 

 area can be noticed. Apart from the slight sinus, the outer form of the 



