REPORT ON THE HOLOTHURIOIDEA. 13 



the latter species they vary in number as well as in position. The dorsal lobe seems 

 to arise exclusively from the anterior part of the back, as in the genus Peniagone, or 

 constitutes a rather broad brim round the anterior flat extremity of the body, as is 

 the case in Scotoanassa and Enypniastes. It might seem as if these two forms of dorsal 

 appendages should offer particularly valuable generic characters by representing the animals 

 in very different aspects, but it must be noted that a series of gradations is to be found 

 between the lobes and the conical processes. I am of opinion that Kolga hyalina, &c, 

 is a striking example, in having its processes disposed in a transverse row, and united at 

 their base, thus running out from a low ridge. 



The calcareous deposits of the integument represent several types, also suitable for 

 drawing lines of demarcation between the genera. The four-armed deposits, being the most 

 common, are found in Parelpidia, Elpidia, Scotoanassa, and Peniagone, — excepting 

 Peniagone naresi, — and resemble one another so closely, that no important peculiarities 

 are to be found among them. Besides, these deposits which sometimes, as for instance in 

 Elpidia glacialis and Elpidia ambigua, are associated with small wheel-shaped bodies, 

 seem to be of little or no value in defining species. With regard to the four-armed 

 deposits of Elpidia glacialis they certainly differ very considerably from all others of 

 the same kind, though constructed after the same idea. The three-armed bodies are 

 found in Achlyonice, Scotoplanes insignis, Scotoplanes robusta, and Peniagone naresi, — 

 the latter possessing besides those C-curved spicula, otherwise exclusively characteristic 

 of the genus Scotoplanes. I do not attach so much importance to the three-armed 

 shape of the deposits as to feel justified in associating the above-mentioned forms with 

 one another. Kolga and Irpa are very closely allied to one another, and have 

 very small horseshoe-shaped spicula, which are peculiar to them. I do not think it 

 possible to found the determination of genera on the form of the calcareous bocbes 

 alone, and I consider the value of the characters which they present to be of necessity 

 subordinate to those depending upon the number of the tentacles, the form of the body, 

 and the conformation of the dorsal appendages ; it is of comparatively slight importance 

 if a species is seen to agree as to its deposits more closely with another genus than with 

 the other species of its own genus. 



The madreporic canal offers distinctions which seem to be most applicable as generic 

 characters. It is either connected to the inside of the body-wall, as in Irpa and 

 Elpidia glacialis, or it pierces it, thus communicating with the exterior, as is the case 

 with Kolga hyalina and several other species. From want of materials, however, I have 

 not been able to examine the madreporic canal in all the different species, wherefore I am 

 obliged to neglect taking it into account in the classification. I know with certainty 

 no other forms than Irpa and Elpidia glacialis in which the madreporic canal is con- 

 nected to the body- wall and does not communicate with the exterior. It is, however, 

 remarkable that these two modes of termination of the madreporic canal, though of the 



