the Echinodermata of the Arctic Expedition. 463 



by any means extravagant when the great irregularity of 

 these parts amongst arctic forms is taken into consideration. 



Ophioglypha rohusta (Ayres), Lyman. 



OpJiiolepis robttsta, Ayres, Proc. Boston Soc. Nat. Hist. iv. p. 134, 



1851. 

 Ophittra fascienlata, Forbes, Append. Sutherland's Joui'nal. 

 ? O. glacialis, Forbes. 

 O. squamosa, Liitken, Vidensk. Meddelelser, Nov. 1854, et Add. ad 



Hist. Opbiuridarum, p. 40. 

 Ophiofihjpha rohusta, Lyman, 111. Cat. Mus. Comp. Zool. Harvard, i. 



p. 46'; Ljuugman, Oph. Viv., CEf. K. Vet.-Akad. Forh. 1866, p. 308. 



Coll. Feilden: Discovery Bay, 25 fms., hard bottom 

 Richardson Bay, 70 fms. ; Hayes Point, 35 fms., bottom-tem- 

 perature 29°*5, and also at 25 fms. ; Franklin-Pierce Bay, 

 15 fms., bottom-temperature 25°"5. 



Coll. Hart : " Winter quarters," Discovery Bay ; Franklin- 

 Pierce Bay, 13-15 fms., bottom stony. 



AnOphioglyptha with arms very finely tapering, and disk with 

 regularly arranged scales of nearly equal size. Mouth-shields 

 ovate shield-shaped, length less than, or at most only equal 

 to, their breadth ; length much less than the distance fi'om 

 the margin of the disk. Papillje of the disk-incision very 

 short and stout, often grouped. Under arm-plates broadly 

 heart-shaped ; one tentacle-scale. 



This species was obtained at various stations, as indicated 

 in the list of localities ; and though neither the abundance nor 

 the size of the specimens was remarkable, several good series 

 were collected. The characters which have been regarded as 

 "specific" are remarkably constant; and no essential difference 

 can be traced between these arctic forms and specimens taken 

 from the coast of Maine, U. S., with which they have been 

 compared, excepting that in the northern Ophiurans the arm- 

 spines are longer and somewhat more delicate, and that the 

 outer margin of the under arm-plates is more arched and the 

 reentering angle is far less developed, in certain species being 

 even altogether untraceable. In some large examples the 

 upper arm-plates are very markedly hexagonal. 



Although this deviation is very constant, the foundation of 

 " a variety " on the strength of such characters alone is hardly 

 justifiable. 



The arm-spines are moderately stout and tapering, the upper 

 one being flattened and much larger than the others. 



In most of the specimens under present consideration, the 

 under arm-plates are well separated from one another by the 

 side ])lates and do not overlap, although in one individual 

 from Discovery Bay the fir.st ten impinge distinctly in conse- 



