14 Echinoderma. 



plates of some Porcellanasteridae are marked by small segmental pits, 

 guarded by moveable lid-like papillae and containing a dark coloured substance. 

 -Terrier's Caulaster is a young Porcellanaster, and its so-called dorsal peduncle, 

 supposed by Perrier to be homologous with the stem of a Crinoid, is merely an 

 extraordinarily developed anal funnel. It is well seen in a very young P. eremicus 

 sp. n., springing from a small membranous space in the centre of the disk, which 

 is enclosed by the dorsocentral and 4 of the 5 large plates which represent the 

 under-basals of a Crinoid. Outside these are 5 smaller basals just as in Caulaster. 

 In the Zoroasteridae the primary apical plates of the larval Echinoderm, dorso- 

 central, basals, and radials, persist in the adult, some species also having under- 

 basals. - The nidamental cavity of the Pterasteridae is formed by a supra- 

 dorsal membrane which is supported by the abactinal paxillae. A network of 

 fibrous, often muscular, bands extends between the spinelets of the latter ; and 

 the supradorsal membrane, occupying its meshes, is pierced by small contractile 

 pores, the spiracula, of which there may be 100 in each mesh. Its central 

 orifice or osculum may be closed by five more or less regular fan-like valves, 

 or simply by a number of webbed or papillose spinelets. At the sides of the am- 

 bulacra are paired segmental apertures, situated at the bases of the long 

 actinolateral spines and opening into the nidamental cavity. They are guarded 

 by small papillae, articulated on the adambulacral plates. - The position of the 

 young of certain species of Asterias in the region of the mouth of the mother is 

 due to the fact that the ovarial tubules are ejected through the actinostomial 

 opening, and that the ova then complete their development in situ, the embryos 

 remaining attached to the mother by means of the primitive connection of their 

 larval organ with the now disintegrated fragments of the ovarial membrane. - 

 There is no reason for regarding the Brisingidae as representing the most primi- 

 tive type of living Starfishes and as presenting a closer approach to the Ophiurids 

 than any other form. They are true Cryptozonate Asterids, very nearly related 

 to the Asteriidae, Pedicellasteridae. Heliasteridae, and Echinasteridae, and pro- 

 bably derived from a common ancestor. The divergence of form and the pecu- 

 liarities of structure now exhibited by Brisinga are the result of modification pro- 

 duced by the extreme isolation and the exigencies of the abyssal depths in which 

 the family has existed. 



Hamann admits that he was wrong in regarding the ganglion ic masses 

 described by Lange above the ambulacra! epithelium of the Starfish arm as groups 

 of connective tissue cells [see Bericht for 1885 I p 189^. They are really of a 

 nervous nature as in Ophiurids, and a similar structure occurs in the radial nerves 

 of Synapta. 



Bell (*) mentions an example of Luidia Sacignii which is probably the largest 

 known Asterid. The disk is 95 mm in diameter and the arms 350 370 mm long 

 with a maximum breadth of 5 Omni. 



Loriol ( 2 ) describes a fossil Anthenea from Algeria in which valvular pedi- 

 cellariae 2mm long are preserved. 



IV. Ophiuroidea. 



See also Bury, supra, p 4, Cuenot. supra, p 6, Fewkes ( 2 , 3 ), supra, p 7. 

 Korschelt ('), supra, p 3, and Semon (' , supra, p 5. 



Hamann reasserts the segmented character of the radial nerve bauds in 

 Ophiurids. Each consists of a mass of fibrils between two layers of cells, that on 

 the dorsal side being separated from the fibrils by a hyaline membrane and also 

 containing fine fibrils. This part, Lange's nerve, is distinctly segmented, the 



