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



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

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

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

 somewhat as in Ophiolepis ; 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 still more flaring, with two great lobes covering the places where the tentacles 

 usually are. 



Species of Ophiolipus not herein described. 



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



Ophiolipus Agassizii, Lym., Bull. Mus. Comp. Zool., vol. v., part 9, p. 220, pi. iii figs. 52-54, 

 1878. 



Gulf of Mexico ; 118 fathoms. 



Ophiomastus. 

 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 

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

 Small 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 bones, 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. 



Ophiomastus tegulitius, Lym. (PL VIII. figs. 16-18). 



Ophiomastus tegvlitius, Lym., 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. 



