544 TAGE SKOGSBERG 



Medial bristles: These are all simple and bare. Somewhat inside and about parallel to the above- 

 mentioned string of pearls a distinct and dense row of fine, comparatively short bristles runs 

 along the anterior part of the dorsal margin of the shell. Somewhat inside and about parallel 

 to this row of bristles another row of bristles runs, continuing down towards the point of the 

 rostrum along the posterior edge of the rostrum — this edge is not distinctly marked, however; 

 this row of bristles is partly rather sparse and also less distinct ventrally; its dorsal bristles are 

 rather short and fine, its ventral bristles somewhat longer and more powerful. Basally on the 

 outside of the selvage a series of comparatively long and powerful bristles issues along the anterior 

 and ventral margins of the rostrum; this row of bristles is rather dense, even very dense along 

 the ventral margin of the rostrum. Besides the bristles so far mentioned there are scattered 

 on the rostrum abundant more or less long and powerful bristles. Basally on the outside of the 

 selvage a relatively dense series of comparatively long and powerful bristles issues along the 

 whole ventral margin of the shell from the incisur to a short distance behind the wreath of hairs 

 round the posterior part of the shell; this row of hairs continues on the ventral lip of the incisur 

 to the outside of the ,,heel". From the incisur to about a third or a half of the distance along 

 the shell the jjart between the bristles in this series bends outwards into a semi-circle; posteriorly, 

 on the other hand, there is no such undulation. ( )n the list there is a rather dense series of bristles 

 varying in length along the whole ventral margin of the shell; along the posterior margin of 

 the shell the list is armed not only with bustles but also with a number of hyaline spines (this 

 part of the list was very defective in the specimen I investigated). On the part between the list 

 and the margin of the shell there seems to be a series of comparatively short bristles inside the 

 ventral part of the posterior margin of the shell. Apart from this there seem to be scarcely 

 any bristles here at all. The selvage is well developed along the whole of the anterior and ventral 

 margins of the shell ; it is moderately wide, has a smooth margin and is partly finely striated. 

 The list is narrow along the ventral margin of the shell, somewhat wider along the posterior margin. 

 For the fixing spots of the shell muscle see fig. 3. The left valve differs from the right in the 

 following respects: The ,. string of pearls" inside the anterior part of the dorsal and the dorsal 

 part of the anterior margin of the shell is absent. The semi- circular convexities between the anterior 

 bristles in the series within the ventral margin of the shell are absent or are very weakly developed. 

 On the part between the list and the margin of the shell there are <i moderate number of fine 

 bristles, varying in length, scattered along the ventral side of the shell. Inside the anterior 

 part of the dorsal margin of the shell the selvage is split up into fine hairs at the margin. 

 First antenna: — This is rather long and slender, but powerful. It has six 

 joints, the third and the fourth joints are free, the original sixth, seventh and eighth joints, 

 on the other hand, are united, although the original boundaries between them can still be 

 j^artly traced and on the lateral side the boundary between the sixth and seventh joints is even 

 partly fairly well developed. The three muscles that move the seventh joint in the genus 

 Aaterope are well developed in this form as well and are attached posteriorly about half way 

 along the definitive sixth joint on a common thickening of the chitinous wall. The relative length 

 of the joints is shown bv the following figures: 



i;;:; 11^:; mV; IV ^ ; V'; VI (orig.) :; Vll (orig.) }. 



