6o ECHINOIDEA. I. 



The blade is filled b>- an exceedingl\- dense and complicated net of meshes. In the fignres of 

 Agassiz (PI. XLI V. Figs. 25— 26, Chall. Ech.) this net of meshes is not seen, but otherwise these 

 figures give a good representation of the single valve. The length of the head i'S""", the neck very 

 short, the stalk thicker aud strenger than usual, with a constriction above. They seem only to be 

 found on the actinal side. Agassiz further figures (PI. XLI V. Fig. 27) a .single valve of a small 

 short-headed, shortstemmed pedicellaria , which seems to be au ophicephalous oue. This form I have 

 not fouud in the .specimen I examiued in British Museum (Chall. st. 2Cxd); but as, at the time, I had 

 not noticed the mentioned figure, I have not, of course, made any special search for it, and so I dåre 

 say nothing of it. If this species should thus prove to be possessed of two kinds of pedicellariæ, to 

 which nothing corresponding is found in any other known Echinothurid, there might be some reason 

 to establish a separate genus for it. For the present, however, I think it most correct to refer it to 

 the genus Hygrosoiiia , as in so nian\- important structures it agrees exacth- with the other species 

 referred to this genus. 



The last of the Echinothurids described from ; Challenger>, PJiormosonia asterias^ differs to a 

 high degree from all the others; to be sure, its peculiarities do not appear from the description of the 

 species by Agassiz (Chall. Ech. p. 104), but his figures give more information, and the examination of 

 the type specimen in British Museum revealed still more interesting features. — The ambulacral areas 

 show tlie quite unique feature that the small secondary ambulacral piates are wanting; there is onlv 

 oue tube foot for each ambulacral plate. Thus only a single series of tube feet is found, and the 

 distance between the feet is rather large. This highly interesting feature is seen very well on the 

 figures of Agassiz (PI. XII. a. Figs. 8, 9); in the description he only says that <;the course of the 

 poriferous zone is quite sporadic. (It is a matter of course that this very interesting feature ought 

 to be examined exactly, as it is possible that traces may be found of the secondary ambulacral piates 

 and their tube feet.) The spicules are lengthened, narrow, with fevv or uo holes (comp. PI. XI. Fig. iS); 

 they are arranged parallel to the longitudinal axis of the foot, in 2—3 well separated series; in the 

 outer part of the foot they ma>- join completely. No sucking disk is found. — The spines are of a 

 quite peculiar .structure, that is to say they are flat and broad towards the point (PI. XIV. Fig. 29). 

 I can give no information whetlier a hoof is found on the point of these spines or on other spines 

 of common form, as I have not made sufficient notes on this faet. The pedicellariæ are not less 

 peculiar. The blade of the tridentate pedicellariæ (PL XIII. Fig. 9) is rather flat, with a more or less 

 well developed, perforated cover-plate below reminding of that in the triphyllotis pedicellariæ. The 

 point is hastately cut off, a little widened, with finely dentate outer edge; the apophysis and the lateral 

 edges more or less thornw In the triphyllous pedicellariæ the cover-plate is very slightly developed, 

 highh- perforated (PI. XII. Fig. 12). The edge shows only very slight indications of teeth, so that they 

 are onl}- to be seen under especialh- high magnifying powers. The stalk of the pedicellariæ is quite 

 different from that of all other Echinothurids, as it consists of long, thin calcareous threads, almost 

 without any coimection except in the upper and Iower end of the stalk — as in au Echinus. It is 

 evident that this species cannot be referred to any of the other genera; it must form a separate genus, 

 for which I propose the name of Kamptosoma'). 



^) xd/xTrnu — Ijend. 



