332 A. E. Verrill — jVbrth American Ophiuroidea. 



Group E. — OpMentrema, sub-gen. nov. Type, 0. scolopendrica (Lym. ). 



Tentacle-pores and scales on one, or a few, basal joints and larger 

 than usual,* farther out decreasing rapidly to a small or rudimen- 

 tary size. Disk-scales concealed by granules. Radial shields some- 

 times partly exposed. Spines numerous, nearly smooth. Mouth- 

 parts as in typical OpMacantha. 



0. granulosa (Lym.). Radial shields largely exposed, broad, in 

 contact distally. Arm-spines ten, slender, the rows nearly approximate 

 dorsally. Tentacle-poi*es of the first joint large, with one flat scale; 

 of others small, with a narrow scale. Dorsal arm-plates all separate. 

 Pacific. 



O. scolopendrica (Lym. '83). Radial shields nearly concealed, close 

 together. Arm-spines seven, unequal, the rows not approximate 

 dorsally. Tentacle-pores large on four joints, with a small scale, 

 rudimentary or lacking distally. Dorsal arm-plates joined on a few 

 basal joints. European. 



Group F. — Ophiomitrella Vei'., 1899a, p. 39. Type, 0. Icevipellis 

 (Lym.). 



Disk-scales visible, bearing granules or spinules. Radial shields 

 partly naked, not large, wide apart. Arm-spines slender, thorny or 

 serrulate ; the rows approximate dorsally in the type. One tooth- 

 papilla. In the type-species a pair of special, distal, oral tentacle- 

 papillae, on the first under arm-plate,f directed into the mouth-slit. 

 Adoral shields wide. Otherwise the mouth parts are nearly as in 

 typical Ophiacantha. 



0. Icevipellis (Lym., '83). Arm-spines eight, slender, thorny. Disk- 

 scales naked or partly granulated. Upper arm-plates separated. 



Group G. — OphiacantlieUa Ver., 1899rt, p. 39. T^q^e, 0. Troscheli 

 (Lym.). 

 Radial shields naked, long, parallel, in contact b}^ their edges. 

 Dorsal arm-plates largely joined. Three tooth-papilla. Arm-spines 

 nearly smooth. 



* Several species that have been referred to Ophiomitra also have this charac- 

 ter. (See Ophiomitra, section AA, p. 351.) 



f The two papilliform appendages of the first under arm-plate are here sup- 

 posed to be movable, but with the published figures and descriptions it is not 

 always possible to distinguish them from the solid, immovable, crest-like lobes 

 which are present on these plates in the same position in many species, including 

 O. bidentata. Among extralimital species, these papillfe are found in some 

 species, such as 0. serrata Lym. , that have the disk-scales and radial shields 

 concealed. 



