100 THE VOYAGE OF H.M.S. CHALLENGEK. 



radial shield. Although proportionately smaller than in Ophiomusium, the jaws have a 

 similar general form, but are furnished with small, stout peristomial plates divided in two 

 parts. The first three arm bones are discoid, with wings which have marginal grooves, 

 somewhat as in Oj^hiolepis ; those beyond, however, grow longer and longer, with flar- 

 ing projections and a wide longitudinal canal above. Towards the end of the arm 

 they are stiU more flaring, with two great lobes covering the places where the tentacles 

 usually are. 



Species of Ophwlipus not herein described. 

 OpMolipus agassizii, Lym. (PI. XXXIX. figs. 1-3). 



Ophiolqym Agassizii, Lym., Biill. Miis. Comp. Zool., vol. v., part 9, p. 220, pi. iiL figs. 52-54, 

 1878. 



Gulf of Mexico ; 118 fathoms. 



OpMomastus. 



Ophiomastus, Lym., Bull. Mus. Comp. Zool., voL v., part 7, 1878. 



Disk arched and extremely high, covered with a few large thick plates, among which 

 the primaries are conspicuous for superior size. Arms short, with large thick side arm 

 plates. First under arm plate similar to and nearly as large as those beyond. Mouth 

 papillse arranged in a narrow close-set line ; teeth rather slender ; no tooth papillse. 

 SmaU smooth arm spines arranged along outer edge of side arm plates. Two narrow 

 genital openings in each interbrachial space. 



Almost the whole roof of the disk is composed of primary plates, which are of a 

 granular structure and much larger than the subordinate radial shields. The low. flaring 

 jaws and mouth frames are furnished with a single, small, crusty peristomial plate. 

 The massive arm plates enclose small, long, cylindrical arm Ijones, of rudimentary 

 structure, and have a well-marked longitudinal canal on the upper surface. The 

 genital plate is short, wide, and stout, with a spatula-like end, and has a scale of a 

 similar form. 



See Plate XXXIX. fig. 14. 



OpMomastus tcgulitius, Lym. (PL VIII. figs. 16-18). 



Opldomashis tegulitius, Lyin., Bull. Mus. Comp. Zool., vol. v., part 7, p. 104, pi. vi. figs, 167- 

 169, 1878, 



Two very short, stout arm spines. Disk plates swollen and microscopically tuber- 

 culous. Side mouth shield of a pointed ovoid shape. 



