Note on Arctic Palaeozoic Fossils. 261 



Discosoms is a slightly arcuate brevicone Cephalopod characterised 

 by the large size, excentric position and nummuloidal structure of its 

 siphuncle. As suggested by Dr H. A. Foord, it seems to bear the same 

 relationship to Actinoceras that Piloceras bears to Endoceras. 



This genus has been seldom recorded, owing probably to the restricted 

 area of its distribution, since the few species known are all from the 

 Upper Silurian rocks of the North American continent. 



The specimens described here are embedded in the foetid limestone 

 already referred to, and as is the case with many of the Palaeozoic 

 Cephalopods possessing thick siphuncles, the siphuncle only is preserved. 

 Since no trace of the shell can be detected in the matrix, it is probable 

 that it was disintegrated prior to its being embedded. 



Discosorus borealis sp. no v. [Fig. 3]. 



The larger of the two specimens at hand is an arcuate cone 6£ em. 

 long, complete but for a small portion of the apex. The section is circular, 

 and the rate of tapering is about 1 in 2'4. The curvature is considerable: 

 upon a chord of 45 mm. subtending the concave side the highest 

 perpendicular is 6 mm. ( = radius of 45*1 mm.). In the upper part of the 

 siphuncle — where the diameter varies from 15 to 25 mm. — the distance 

 of the segments from each other averages 6 mm., and the segments are 

 in a plane 75° to the axis. A remarkable feature is the sudden change 

 in the position and size of the segments in the apical region, where 

 they are in a plane 60° to the axis, while the distance separating them 

 is only about 2 mm. 



The surface of the segments is rounded and protuberant along the 

 convex side of the siphuncle, and is flattened along the concave side, a 

 character noticed by Dr Foord in his diagnosis of D. remotus. 



The present species is evidently closely allied to D remotus Foord 

 {op. cit. p. 197), and might even prove to be synonymous with it, but 

 since the type of Dr Foord's species is too fragmentary to permit of close 

 comparison, the two forms are better kept under a separate designation. 



Discosorus regularis sp. nov. [Fig. 1], 



This species is known by three specimens of the siphuncle. The 

 best preserved is an arcuate cone 9 cm. long, the apex of which is 

 wanting. The section is circular and the rate of tapering is about 1 in 

 2 - 14. The curvature is less than in the preceding species : upon a 

 chord of 50 mm. subtending the concave side the highest perpendicular 

 is 4 mm. (=80 mm. radius). The distance separating the segments is 

 6 mm. where the diameter is 30 mm., and decreases slightly and gradually 



