94 



than with this genus itself. In any case we must consider the genus Brisinga, in respect 

 of the general composition of the body, as the most primitive and therefore the oldest of 

 all Echinoderms. 



8. 

 Comparison of the i species of Brisinga. 



The two hitherto known species of the genus Brisinga, Br. endecacnemos and Br. 

 coronata, stand in close connexion, but exhibit nevertheless certain distinctive characteristics 

 which make their specific distinction necessary. The latter of these species has already 

 been exhaustively described in the foregoing pages. As regards the first species discovered, 

 Br. endecacnemos, its general appearance and structure are pretty well known from Asbjom- 

 sen's description and figures. It might possibly however not be without interest here to 

 notice again this species, and to compare it with the Br. coronata. I have therefore added 

 a plate (Tab. VII) in illustration; and will now briefly point out the characteristics wherein 

 the two species differ from each other. 



In size, color and general habitus they are (see Tab. VII, fig. 1) nearly similar. But 

 an important distinctive characteristic is the number of the arms or rays. While this num- 

 ber is in the Br. coronata, as previously noticed, extremely variable, the number of rays in 

 the Br. endecacnemos has already become completely permanent, and is constantly 11. In no 

 single one of the numerous specimens which have been examined of this species, (and their 

 number far exceeds that of the specimens taken of the other species), has there ever been 

 noticed any deviation from this rule; for which reason also the specific denomination Ende- 

 cacnemos is fully justified. The manner in which the arms are inserted on the disc is 

 completely similar in both species. Still the interval between the bases of the arms 

 is in the Br. endecacnemos still more restricted; so that the arms nearly touch each other 

 at the base; while we always find in the Br. coronata an evident, even if only a small 

 interval. 



The disc is, viewed from above (see fig. 1) in both species circular; seen from the 

 side (fig. 2) it appears however in the Br. endecacnemos somewhat higher than in the other 

 species, and has its exterior border more perpendicular. The disc-spines, (fig. 6) are nearly 

 similar to those in the Brisinga coronata. They stand usually still more closely together: 

 and the proper calcareous spine exhibits at the extremity only a few secondary spines. The 

 shape of the madreporic body (see fig. 1, 2 & 4) is characteristic for the Br. endecacnemos. 

 It is always remarkably prominent; so that when the disc is viewed in profile (fig. 2) it pro- 



