ECHINOIDEA. I. ^z 



spille; it is very large and couspicnous in some species, as /V/. Iioplacantha^ Spcrosoma Grimaldi/ a. o., 

 small in Asthcnosoma Grnbct\ hysfrix a. o. These spines are always (?) more or less curved. — In a group 

 of species: Plioriiiosoina placenta^ bnrsariiuu, and rigidiiin (a. o.?) the primary spines of tlie actinal side 

 are surronnded b)- a bag of skin, and their points are swoUen in a chib-shaped way. In Asthc7iosoina 

 Gr7ibn\ varimii, hctcractis, and urens the spines on the abactinal side, primar>- and secondary ones, are 

 inclosed b\- a thick cutaneous sheath which is constricted one or several times; also in other Echino- 

 thnrids, for instance A. hystrix, small bags of skin are seen at the point of the small spines. These 

 spines are distinctly distinguished from the mentioned skin-covered spines in Pli. placenta^ bursarinm, 

 and rigidum by being constnicted as nsual — simple perforated tnbes with a long, fine point, while 

 in Ph. placenta etc. they are swollen at the point, and filled by an irregular calcareons net of meshes. 



The tnbe feet may be arranged in an almost straight line on the actinal side, as in Ph. pla- 

 centa, or they ma}- be trigeminous, about as in an Echimis, as for instance in A. hystrix, or they may 

 be arranged in three widely separated series, as in Spcrosoma. In some there is no trace of a snckino- 

 disk on the tnbe feet of the actinal side, in others there is a well-developed disk; on tlie abactinal side 

 a sucking disk is never fonnd. The spicnles are almost always rather large, irregular, fenestrated 

 piates sitnated more or less distincth- in 3 — 4 longitudinal series. In A. var mm, Grube i, hetcractis, 

 and urens they are very slightly developed, onh' small, iManched calcareons pieces, rarely with a hole. 

 — The sphæridiæ, which follow the tube feet quite up on the abactinal side, show no differences so 

 great that they can be of aiu- systematic importance. The pedicellariæ, on the other hånd, are of the 

 greatest importance with regard to the classification. 



No less than 5 different kinds of pedicellariæ are found in the Echinothurids, viz. the fonr 

 kinds known from the Echinids, and fnrther the very beantiful form, described by Wyv. Thomson 

 in A. /enestratum, the te tr adacty Ion s pedicellariæ. Only the tridentate and the triphyllous pedicel- 

 lariæ are found in all Echinothurids, each of the other kinds are only found in a single genus. — The 

 tetradactylous pedicellariæ have been .so excellently described and figured bv Wyv. Thomson, that 

 I need not add anything. Globiferous pedicellariæ were hitherto unknown in the Echinothurids; I 

 have fonnd them in A. pcllucidum (in one of the type specimens from Chall. st. 192; the other speci- 

 mens I have not seen). They are highly primitive; the skeleton consists of three simple rods, a little 

 widened below. No muscles seem to pass between them, which corresijonds very well with the faet 

 that the three glandular bags are quite inclosed b}- a common skin; the pedicellaria cannot be opened 

 as other pedicellariæ. The valves have only half the length of the head, and they are placed between 

 the glandular bags (PI. XIII. Fig. 24). There can scarcely be any doubt that this interesting form of 

 pedicellariæ is to be interpreted as a ver\- primitive globiferous pedicellaria. 



Neither were ophicephalous pedicellariæ hitherto known in the Echinothurids. The form of 

 pedicellariæ figured and described by Wyv. Thomson as ophicephalous pedicellariæ, is indisputably 

 the triphyllous pedicellariæ, very similar to the triphyllous pedicellariæ of the Echinids, only .some- 

 what larger. Genuine ophicephalous pedicellariæ I have only found in the new form Troviikosoma 

 Koehlcri, described liere. They are very characteristic, the blade is highly constricted just above the 

 basal part, and abruptly widened above (PI. XIV. Pigs. 19, 23, 25). The somewhat contorted are on the 

 lower side of each valve, so characteristic of the ophicephalous pedicellariæ, is here ty^jically developed. 



