KONGL. SV. VET. AKADEMIENS HANDL. BAND 19. N:0 7. 7 



has been well compared to that of an inverted short-necked bottle, while in the side 

 view, jig. 3, the front line appears bluntly truncated, and the dorsal line, slightly 

 more convex than the ventral, is sepai-ated from it behind by a deep depression, 

 beyond which the test is ventrally produced in a short, contracted, depressed, and 

 truncated caudal prolongation. The back, in nearly its anterior half, is uniformly 

 vaulted from side to side, in its posterior half rather more convex, and raised along 

 the middle-line into a distinct keel, which is continued and somewhat more prominent 

 on the caudal prolongation. The ventral surface is slightly tumid a little before and 

 again a little behind the middle. All around the front the test is suddenly bent 

 inward and backAvard, jig. 2, so as to form a deep ovoidal recess projecting into 

 the peritoneal cavity, PI. Ill, jig. 10, 12; IV, 18, 19; and, as this incurvation takes 

 place on the ventral side farther back than on the dorsal, or at about one sixth of 

 the entire length and a little behind the stoma, the ventral margin of the recess lies 

 at the hindmost part of a parabolic depression or sinus, the depth of which seems 

 to vary somewhat. At its bottom and close within the ventral margin is the oeso- 

 phageal opening of the alimentary canal, PL 111, jig. 12; IV, 18, 19, 20. 



The excretory opening is at the bottom of 

 the hinder depression, PI. 1, jig. 4; 111,- 13, und 

 the stomo-proctic axis makes an acute angle with 

 the antero-posterior and longitudinal axis. 



The whole of this anomalous configuration 

 appears, as though it were the result of the dorsal 

 portion of the body having moved forward beyond 

 the normal measure, and so as to leave behind 

 the subanal part of the ventral portion, and as \ 

 though its forepart, produced into a rostrum 

 projecting ventrally and compressed from both \ 



sides, had been drawn in, by invagination, into 

 the peritoneal cavity, its bridge thereby having The imaginary rostrum 



become the highest part of the hollow thus formed. mvagma u pio m mst. 



The vertical transverse section of the test, a little behind its middle, is somewhat 

 elliptic and slightly higher than broad, the dimensions of the whole being 



Specimen 1. Sp. 2. Sp. 3. Wyv. Thomsons sp. 



Length 36 mm. 34 mm. 31 mm. 45 ram. 



Breadth 18 » 18 » 15,5 » 18 » 



Height - 19 » 19 » IG » 20 » 



The greatest breadth lies a little higher up than the hjngitudinal axis, and the 

 greater half of the section therefore belongs to the ventral surface. 



The lengthened body and its nearly circular section distantly recall the cylindroid 

 form of the Holothurite. Among the Echinoids the Spatangi alone offer anything like 

 it, although the resemblance at last turns out slight enough. Nor is it to their oldest 

 forms that we have to go in search of it. On their first appearance, as the Cretaceous 



