1 8 Echinoderma. 



expansion (ridge, D. & S.) are three sutures, one median and two lateral, in ad- 

 dition to others at its edges, which are interpreted by Duncan & Sladen as inter- 

 radio-ambulacral. For they are very distinct in two other specimens examined 

 by those authors, and show that no part of the ridge is ambulacral, all being 

 interradial ; but no median suture is visible in either specimen. D. & S. now hold 

 that no portion of an ambulacrum exists on the flanks of the interradial expansions, 

 that ambulacral processes or their homologues are absent, but that the expansions 

 are analogous to, and to a certain extent homologous with, the ridges of Cidaridae 

 [see Bericht for 1886 Ech. p 11]. Unlike Loven they can find no evidence in 

 favour of the existence of jaws and teeth either in Discoidea or in Echinoconus. 



Duncan (*) notices some interesting points in the anatomy of Palaechinus . In 

 P. sphaericus the radial plates of the apical system sometimes enter into the ring 

 of basals , but are altogether outside it in other individuals , not reaching the 

 margin of the periproct. The plates of the ambulacra are low, very thick, and 

 variable in shape in the same ambulacrum. There is no overlap of the interradii 

 over the ambulacra, the test being as rigid there as in an Echinus. Five species 

 have the pairs of pores biserial on each side of an ambulacrum. In P. gigas and 

 ellipticus the outer pairs of pores of the vertical rows are in demi-plates ; while 

 in P. sphaericus, intermedius, and Phillipsiae, the plates of both sets of pairs of 

 pores are primaries, some being blocked out from the lateral sutures. The forms 

 of P. with uniserial pairs of pores should be referred to Rhoechinus. 



Gregory ( 2 ) describes a new Cystechinus (crassus) from the Radiolarian Marls of 

 Barbados. The test is composed of unusually thick plates, with a striking simi- 

 larity in structure to that of the Palseechinoidea. In both the tests are flexible, 

 composed of hexagonal plates, provided with apetaloid ambulacra, with a single 

 pore in each plate of the ambulacra, and an epistroma of minute granulation with 

 small sparsely scattered tubercles exactly like those of some Perischoechinidae, 

 such as Palceechinus. 



Bell ( 2 ) shows that Stewart's organs are not so largely developed in the 

 Echinothuridae as supposed by the cousins Sarasin [see Bericht for 1888 Ech. 

 p 22]. For they are sometimes absent in Phormosoma, and sometimes only pre- 

 sent in a rudimentary or vestigial condition, while they seem to be absent in 

 Asthenosoma Grubii and A. pellucidum. The former has well developed longitu- 

 dinal muscles, but they are small in A. pellucidum and absent in Ph. The large 

 size of Stewart's organs and of the longitudinal musculature is not therefore such 

 a general distinctive character of the Echinothuridae as stated by the Sarasins. 

 The latter authors give a re'sume' of the palseontological questions discussed in 

 their large work on the Echinothuridae [see Bericht for 1888 Ech. p 23]. They 

 criticise Neumayr's view that the Echinothuridae are modified descendants of the 

 Diadematidae, and only have atavistic resemblances to the Palaeechinoidea ; for 

 Duncan (*) has shown that some of the triple plates of Palceechinus are very 

 suggestive of those of the later Echinothuridae. 



Ebert gives a detailed account of the changes during growth in the test of 

 Maretia Hoffinanni. They affect more especially the external form, the shape of 

 the ambulacra which are less petaloid in the young test, the development of inter - 

 ambulacral tubercles, and the sculpture of the under side. A detailed knowledge 

 of these growth stages is important, as some of them have been made into new 

 species. 



