180 PROF. F. JEFFREY BELL ON THE [Mar. 1, 



ossicles articulate with one another by means of a more or less 

 simple ball-and-socket joint ; the covering plates are more or less 

 regularly developed as superior, inferior, and two lateral, the last of 

 which bear spines. 



The Astrophiurae (s. Cladophiurse) are Ophiurids in which the 

 ambulacral ossicles articulate with one another by means of hour- 

 glass-shaped surfaces, and are covered by granular deposits in the 

 thick integument ; the arms may be simple or branched repeatedly. 



The Zygophiurse are Ophiurids in which the movement of the 

 ossicles on one another is limited by the development of lateral 

 processes and pits ; superior, inferior, and lateral spine-bearing plates 

 are always developed as a covering for the arms, which are always 

 simple, and incapable of coiling round straight rods. 



TJie StreptopMurce. 



The following facts justify the vagueness of the definition offered. 



a. Upper arm-plates : absent in Ophiomyxa vivipara, double in 

 O. pentagona, of several pieces in O. jlaccida ; double in 

 Opliioteresis ; in Hemieuryale a mosaic of small plates ; single 

 but incomplete in Neoplax. 



j8. Under arm-plate : absent from Ophioteresis, alone among existing 

 Ophiurae. 



y.' Tentacle-scales : absent from Ophiomyxa, Neoplax, and 

 Ophiobyrsa. 



2. Tooth-papillce. : absent from Sigsbeia, Hemieuryale, Ophiochon- 

 drus, and Ophiomyxa. 



e. Radial shields are small and short in Ophiobyrsa, small and 

 irregular in Ophiomyxa, rather large in Ophioteresis, large in 

 Hemieuryale, and very large in Sigsbeia ; on the other hand, 

 they are absent from Neoplax. 



The order in which the genera just mentioned should stand to one 

 another is a question which cannot be discussed now, nor can that 

 of the relation, clearly enough marked in many points, between the 

 Streptophiuree and the lowest of the Zygophiurse : the "articulating 

 peg " in Ophioscolex is described as minute ; it, Ophiambix, Ophio- 

 sciasma*, Opliiogeron*, Ophiohelus*, and OphiothoUa have no upper 

 arm-plates, while in Ophiomyces they are, if present, minute ; in the 

 three genera marked with an asterisk the arm-ossicles retain the 

 embryonic character of being nearly divided into two. 



In addition to the genera placed under the " Astrophyton-like 

 Ophiurans " of Mr. Lyman — Ophiobyrsa, Ophiomyxa, Ophiochon- 

 drus, Hemieuryale, and Sigsbeia — to which, of course, must be added 

 Neoplax, I would place in the Streptophiurae the genera Ophio- 

 myces, OphiothoUa, Ophiohelus, Ojihiosciasma, Ophiambix, and 

 Ophioscolex. 



Mr. Lyman says of Ophioblenna, which he places next to Ophio- 

 scolex, " Of its skeleton I am quite ignorant." I applied, therefore, to 

 Dr. Liitken, who has charge of the only known specimens, and he 



