38 OLAF HOLTEDAHL. M.-N. Kl. 



Brachyprîon explicatum n. sp. 



(PI. IV, figs. 2-5.) 



Mat. pres. A few, fragmentary ventral valves, and a larger number 

 of outer moulds of dorsal. 



Description. Adult specimens of a rather large size, oudine 

 semicircular, without strongly pointed cardinal extremities. The following 

 figures give in mm. width and length of some specimens measured: 



Width 22^/9 47 60 

 Length 14 28 34 



Also relatively longer and narrower specimens occur. Convexity 

 moderate, or only very slight, dorsal valves may be very nearly flat. 

 In the ventral valves the convexity is more even, dorsal valves when 

 expressly curved are more geniculated with a deflected marginal portion. 



Surface markings nicely preserved in a number of specimens. The 

 radiating striae are of two distinct sizes, the stronger one of medium size, 

 rather narrow, but well raised, the finer ones, the number of which in 

 each interspace (that generally has a width of about i mm.) is 2 — 8, being 

 very delicate. The number of primary ribs increases in the ordinary way 

 by a fine one in the middle of an interspace gradually becoming stronger 

 towards the antero-lateral margin. Crossing the radiating ribs in well 

 preserved surfaces we see very fine, crowded concentric, raised lines, 

 running somewhat irregularly and undulatingly. 



No corrugations are visible. Interior characters not known. 



Observations. Though the specimens here described as regards 

 general form show a considerable difference from the species mentioned 

 before, they are no doubt nearly related to it. The more convex speci- 

 mens of the former may indeed be difficult to separate from the flatter 

 types of the latter. 



Many of the specimens of this form strongly remind one of Rafines- 

 quina expansa, but can generally be easily distinguished by more delicate 

 and regularly arranged radiating striation. 



Occurrence. The bulk of the specimens were collected in 8 c 

 in Malmø, Bundefjord. Similar specimens are also found in older beds, 

 in 7 a, Ulve, Bundefjord and in younger, in 9 d. Lange off Holmestrand. 



