114 bulletin: museum of compakative zoology. 



are so rudimentary that it becomes a question of mere personal opinion whether 

 they are present or not. It seems therefore very unwise to attempt to maintain 

 any longer the artificial line which has so long separated Ophiopeza from Pec- 

 tinura. Since the latter genus was established, no less than 34 species have 

 been referred to it; of these, P. f orbed Heller has been made the type of Ophio- 

 conis by Liitken, P. spinosa, Ljuugman is the type of Ophiopezella, and P. verru- 

 cosa Studer has been removed to Ophioglypha by Studer himself; as at present 

 recognized then Pectinura contains 31 species. To Ophiopeza 11 species have 

 been referred, but one of these, 0. custos Koehler, has been transferred by Koehler 

 himself to Ophioplax, so that there are at present 10 species in the genus. If 

 the old distinction between Pectinura and Ophiopeza is abandoned, the question 

 arises are these 41 species congeneric ? By no means ; for with one or two ex- 

 ceptions, they fall very naturally into five groups, regardless of the presence or 

 absence of supplementary oral plates and of the equally inconstant character, 

 pores between the basal under arm-plates. Curiously enough the number and 

 arrangement of the tentacle-scales, a feature which in some other groups is so 

 variable that it is of doubtful value even for distinguishing species, is here re- 

 markably constant, and is so obvious as to make a very serviceable character. Of 

 the 41 species under consideration only eight have a single, conspicuous tentacle- 

 scale, while the remainder have two, the outer one overlapping the base of the low- 

 est arm-spine. Of the eight species with the single scale, one is unique in having 

 the whole oral surface, including the oral-shields, covered with a fine granulation; 

 the other seven (with perhaps one exception) form a homogeneous and natural 

 group of deep-water species. Of the 33 species having two tentacle-scales ten, 

 including the type of Pectinura, have the radial shields concealed by the granula- 

 tion of the disc, and as this appears to be a very constant character the name 

 should be restricted to this group. One of the remaining species is quite unique 

 in its very large, bare, radial shields and wide arm-bases, and as it has twice been 

 made a generic type, it may well stand by itself. Por the rest of the 22 species, 

 Ljungman's old name Ophiarachuella is available and should be used. The chief 

 objection to this grouping is that Peter's familiar name Ophiopeza becomes a 

 synonym of Pectinura. It is unfortunate, but in view of the inconstancy of the 

 character upon which the genus is based, this result cannot be avoided. 



In the examination of the M. C. Z. collection, I have found two undescribed 

 species of this group. I have also found that some of the hitherto recognized 

 species cannot be maintained. I give therefore the following artificial key to the 

 genera which have been under discussion, and a list of the valid species under 

 each genus with artificial keys to the same. The essential synonymy of each 

 genus and species is also included. 



Key to the Genera. 



Oral shields distinct, not concealed by any granulation. 



Tentacle-scales 2, at least on basal part of arm, with outer over- 

 lapping base of lowest arm-spine. 



