REPORT ON THE OPHIUROIDEA. '247 



Ophiochondrus. 



Ophiochondrus, Lym., Bull. Mas. Comp. Zool., vol. i., pnrt 10, 18G9. 



Teeth. Mouth papilla?, which are about seven and are short and crowded. No tooth 

 papillae. Disk granulated ; contracted, so that the interbrachial spaces are re-enteringly 

 curved, and are further reduced by the encroachment of the stout arms, which roll in a 

 vertical plane. Four to six small, smooth arm spines. Side mouth shields meeting within. 

 Side arm plates meeting below, and there closely soldered. Two genital openings in each 

 interbrachial space. 



One is surprised to find so powerful a frame in animals whose exterior seems scarcely 

 to indicate peculiar strength. The thick disk skin, granulated above, is set below with 

 stout, irregular plates, and supported by long, thick, bar-like, solid radial shields (PI. 

 XLIII. fig. 11, I). To these are articulated massive, shapeless, genital plates (o), a full 

 half of whose length is occupied by the clubbed head, while the comparatively small shaft 

 is rounded and tapering. About half-way of its length there is soldered to it a small, 

 rounded genital scale (n). Not less thick and strong are the large transverse oval 

 peristomial plates (v), which, usually single, but sometimes divided in two, nearly touch 

 each other by their proximal corners. Within the disk the arm bones are plain and 

 discoid ; but beyond the margin they take on a curious elongated shape (w). Their 

 outer face has a wide massive articulating shoulder (fig. 12, 4) to support the large umbo 

 of the next bone (fig. 13, 1) the articulating peg (6) is small and has no distinct hole for 

 its reception in the next bone. From above, the bone (fig. 15) is seen to be massive, 

 widest within, and with a well-marked median canal (t') ; from below (fig. 14), it has a 

 similar outline, with a very deep canal (t) having rolling margins, large, deeply excavated 

 muscle fields (10), and small tentacle sockets (r) quite at the outer end. The great length 

 of these arm bones gives them an embryonic character, found also in Ophiomusium. The 

 inner face shows a slight leaning towards Astrophyton, but on the whole they are truly 

 Ophiuran in structure. 



Ophiochondrus stelliger, Lym. (PL XXI. figs. 13-15); Bull. Mus. Comp. Zool., vol. 

 vi., part 2, p. 44, pi. xiii. figs. 371-373, 1879. 



Disk finely and evenly granulated on both sides. Four slender arm spines, whereof 

 the uppermost is much the longest. 



(Type specimen from Station 320.) Diameter of disk 5 mm. Length of arm 16 mm. 

 "Width of arm near disk 1'3 mm. Three mouth papillae on each side, whereof the two 

 outer are flattened and squarish, while the innermost is stout, rounded, tapering, and peer- 

 like. Apex of mouth angle occupied by the lowest tooth, which is sometimes represented 

 by two blunt, spiniform papillae similar to their next neighbour. Four rather narrow 



