38 



are verj' similar lo those of A. lonsiim. The ojjhicephalous pedicellariæ occur in a 

 large and a small form. The large form (PI. IV. Fig. 8, PI. V. Fig. 4) has Ihe valves 

 rather elongate, as those of A. Jacobyi, but they are not so large as in thai species; 

 they are filled with an irregular meshwork, and the outer end of the valves forms 

 a hook, especially large on one of the valves (see PI. V. Fig. 4). The small form 

 occurs both with glands on the stalk (PI. IV. Fig. 33) and without such glands (PI. V. 

 Fig. 32); in both of them the upper end of the stalk is cupshaped. The valves 

 (PI. III. Fig. 18) are simple, without meshwork; the outer edge is somewhat sinuate, 

 the whole form somewhat dilTerent from those of the ]U-eeeding species. 



Dermatodiadema indiciim Doderl. and umphigijmmim de Meijere have been 

 carefully treated by de Meuere (Siboga-Echinoidea p. 46 seq.); they prove to be 

 essentially like the above mentioned species as regards pedicellariæ and spicules; 

 the tridentate pedicellariæ of D. indiciim are like those of D. microtiibercnldtiim, 

 those of D. amphigymniim are unknown, the tridentate pedicellariæ mentioned under 

 this species by de Meijere being the large ophicephalous pedicellariæ. D. molle 

 Döderl. has tridentate pedicellariæ like those of microtuherciilatiim (Prof. Dödeiu.ein 

 has kindly allowed me to examine the pedicellariæ of this species during my visit 

 in Strassburg); otherwise it does not present important characters in its pedicel- 

 lariæ. — The species D. globiilosiim Ag. and horridiim Ag. I have not seen. 



The genus Dermatodiadema has been established by Ar.Assiz („Albatross"- 

 Echini 1898. p. 76) for the species „having only small secondary tubercles in the 

 ambulacral areas'-; accordingly the species microliiherculaium and untillarum must 

 be transferred lo that genus; de Meijere also rightly names these species Dermato- 

 diadema. This dirterence in the ambulacral tubercles is indeed the only character 

 distinguishing the two genera, and as there may be found an indication of larger 

 primary ambulacral tubercles in species with small ambulacral tubercles, this 

 character is evidently of little value. The pedicellariæ do not afford generic 

 characters; only the tridentate pedicellariæ present two distinct types, but as both 

 these types occur in both the genera, no generic character can be taken from them. 

 — PoiMEL ') has established in 1883 the genus Plesiodiadema for Aspid. microtiibercii- 

 latiun; this name has then to be used instead of Dermatodiadema. Duncan'-') has 

 later on, 1885, used the name Plesiodiadema for a fossil form, but of course it must 

 be maintained in the sense of Pomel. 



The claviform pedicellariæ of Aspidodiadema and Plesiodiadema are held by 

 Agassiz to be of great value for comparative morphology. „These pedicellariaV, he 

 says in the „lilake'-Echini p. 25, „recall at once tlie remarkable sheathed spines . . . 

 in Asthenosoma (irubei , they form an additional link in the chain proving that 

 pedicellariæ are only modified spines. The diminutive heads of these pedicellariæ, 



') CInssification méthodique et genera tics Echinides vivants et fossiles. 1883. (Doet. ïliesisi 

 ') Quart. Jouni, Geol. Soc. 41. 1885. 



