358 A. M Yerrill — North American Ophixiroidea. 



Externally there are no tangible characters to distinguish this 

 family from certain of the OpJiiacanthidce^ except the lack of upper 

 arm-plates, which are always present in the latter. But the internal 

 structure, so far as studied, is peculiar. 



The family, as here understood, includes the following described 

 genera : OpMoscolex, Ophiosciasma, Ophiogeron., Ophiohyrsa, and 

 Ophiamhix. 



Certain species that have been referred to some of these genera do 

 not agree in structure with the typical species, and therefore I have 

 established two new genera for their reception : 



Ophiohyr sella, gen. nov. Type, Ophiohyrsa serpens Lyman, 



Astrogeron, gen. nov. Type, Ophiogeron siipinus Lyman. 



Ophioseolex fragilis Ver. , sj). nov. 



Five slender arms. Oral shield small, narrow, pear-shaped, with 

 an acute proximal angle. Adoral shields narrow, oblong, the inner 

 end acute and touching. Oral papillae six or seven, forming a row 

 which is not regular in the middle ; the two outer ones are larger 

 than the others, tapered, acute ; the four inner ones, which do not 

 lie in just the same line, are small, slender, acute. Lower arm-plates 

 hour-glass-shaped, narrow, longer than wide, truncated at the ends 

 and closely joined, and apparently soldered with the side plates. 

 Arm-spines three, slender, tapered, acute, nearly equal, about as 

 long as a joint. Tentacle-pores large. No tentacle-scale. The 

 disk is destroyed in my specimens. 



Diameter of the disk-scar, 10'""'; length of arms, 22""". 



Off Barbadoes, Station 293. Blake Exp., 82 fathoms. 



Ophiobyrsella Ver., gen. nov. Tj^pe, O. serpens (Lym.). 



Disk pentagonal, covered entirely by naked skin, which hides the 

 oral and adoral shields and extends out over the upper and under 

 sides of the arms and spines. Small spinules are situated over the 

 region of the radial shields and along the margins of the disk, or 

 over the whole disk. No tentacle-scales ; tentacles large. Arm- 

 spines three to five, — three in the type ; rough, glassy. About five 

 spiniform teeth. Oral papillae form a regular lateral row, besides 

 two or three tooth-papillae at the tip of the jaw. 



This genus is very near Ophioseolex in external characters. 



True Ophiohyrsa (type, 0. rudis) differs in having only one oral 

 papilla, no teeth, and only a few spiniform tooth-papillae ; these 

 parts being very much reduced. 



