ECHINOIDEA. I. 



of wliich ends in a fine pore at the end. The rods reach only half-way, the whole thing is coalesced 

 to the very point; there are no mnscles between the basal parts of the valves. In another genus 

 (Arccosoma) a singular kind of pedicellariæ are fonnd, the tetradactyle, with four pecuHar, very ele- 

 gantly formed valves. Also in other Echinoids a fonr-valved pedicellaria niay now and then be fonnd, 

 but only as an abnormity. Ophicephalous pedicellariæ') are aniong the Echinothuridæ found in 

 only a single genus (Troiuikosonia)\ on the other hånd, triphyllous and tridentate pedicellariæ are 

 found in all of them, and cspecially the tridentate ones show a great variety of forms, and are of great 

 systematic importance. In the Cidarids are found tridentate pedicellariæ, and another kind occuring 

 in a large and a small form, of substantially the same structure. They seem to be poison-apparatus 

 as the globiferous pedicellariæ of the Echinidæ; but they are of a quite different structure, the gland 

 being here placed inside the blade, quite surrounded by the calcareous skeleton, while in the Echinidæ 

 it is situated on the outside of the blade. On the inside of the blade, somewhat below the point, there 

 is a larger or smaller opening (the niouth ) in the calcareous skeleton, filled with large cells, richly 

 provided with cilia (sensitive hairs?). The efferent duet of the secretion of the gland passes up through 

 the end-tooth, and opens on its surface. How these structures are arranged in forms with no end-tooth 

 is unknown. The inner opening is of great systematic importance, while the glandular opening itself 

 scarcely is of any importance in this respect. P e r r i e r (op. cit.) gives these pedicellariæ a special name 

 Pedicellaires armées». After the discovery of the above described form of globiferous pedicellariæ 

 in the Echinothurids^) there seems to be sufficient reason to take these pedicellariæ in the Cidarids 

 to be homologous with the globiferous pedicellariæ of the Echinoids, as has also been done by Stewart 

 (379) ^^^ Prouho (327), so that there is no cause to keep the name given to them by Perrier. 

 There is still less reason to keep the name ■ Ped. inermes > for the tridentate pedicellariæ of the 

 Cidarids; there eau be no doubt but that they correspond to the tridentate pedicellariæ of the other 

 Echinoids (Prouho (327), Koehler (217)). Hamann (184) regards the small pedicellariæ as «a sub- 

 species of the tridactylous ones >. Now it has to be admitted that sometimes it may be rather difficult 

 to distinguish between these latter and small tridentate pedicellariæ; but generally they are very easily 

 recognised, and there is no doubt that, with regard to structure, they resemble very much the large 

 globiferoiis ijedicellariæ. Wliere no pronounced difference is found between large and small pedicellariæ, 

 it may in faet be impossible to decide, whether a certain specimen is to be regarded as a large or as 

 a small form. There seems to be no reason to give a special name to the small pedicellariæ; in the 

 present work they will the mentioned as <;small globiferous pedicellariæ*. — Ophicephalous and triphyl- 

 lous pedicellariæ are not found in the Cidarids. 



O. F. Muller 3) has originally given names to the pedicellariæ, viz. Pedicellaria globifera, 

 triphylla, and triden.s. These names have not been generally accepted, the reason being cspecially 

 that Valentin in his classical monograph on the anatomy of Eclii)ius has used other appellations: 

 Pedicellaire gemmiforme, tridactyle, and ophicephale; these names have become the common ones. 

 SI ad en (366) justly maintains that it is incorrect to use these latter names. The figures of Miiller 



') What has hitherto been regarded as ophicephalous pedicellariæ in the Echinothuridæ, are in reahty triphj-Uous ones. 

 2) Also the globiferous pedicellariæ in Stomopmustcs seeni to fonn a peculiar type. They have no end-tooth, and 

 there seems to be no poison gland on the outside of the blade. 

 J) Zoologia danica. 1788. pag. 16. Tab. XVI. 

 The Ingolf-Eicpedition. IV. I. 2 



