EEPORT ON THE OPHIUROIDEA. 113 



In respect to disk scales and radial shields the arrangement resembles that of Ophio- 

 pholis (especially in Ophiactis asperulu), though other species {e.g., Ophiactis cuspidata) 

 have much larger and stouter scales. There is a resemblance likewise in the peristomial 

 plate which is wanting {Ophiactis kroyeri), or is a mere thin crust {Op>hiactis savignyi), 

 or is small and linear {Ophiactis asperula). The genital plate is usually very stout, 

 though long, slender, and cylindrical in Ophiactis hroyeri, and has attached to it a 

 considerably shorter genital scale. The arm bones are discoid and delicate, with thin 

 wings. 



Table of Species of Ophiactis. 



1st Type. The number of mouth papilla increase with age. 



Six to seven short, thick, blunt rough arm spines. Young usually with six " 

 arms; adult often with only five. Commonly two mouth papillEe on 

 each side ; rarely more. Upper arm plates microscopically tuberculous, 

 swollen, usually with a faint lobe on the outer edge. Radial shields [ Ophiactis savignyi. 

 large, scarcely diverging, nearly or quite touching. Side mouth 

 shields nearly or quite meeting at their outer ends. Numerous disk 

 spiues, . . . . . . . . .J 



Radial shields narrow, oval, and separated. Upper arm plates wider than long, \ 



with lateral sides re-enteringly curved. Under arm i^lates broader than > Ophiactis affinis. 

 long, and cleanly curved without, . . . . . / 



The adult (var. quinqueradia) has five arms; upper arm plates transverse oval, \ 



and not thickened; tliree or even four mouth papUlai on a side. The \ Ophiactis mvlleri. 

 young is like Savignyi (six arms), but has no lobe on upper arm plate, . J 



\ Ophia 



Ophiactis halli. 



Skin thick and much obscuring the scaling and mouth shields. Radial shields i ^ , . ,. , ... 

 narrow and smaU. Five sliort, thick, blunt, flattened arm spines, 



2nd Type. The number of mouth papiUai' seems never to vary. 

 SmaU radial shields, just touching without, widely diverging inward, four stout ■ 



and blunt, but cylindrical and tapering, arm spines. Disk scales curved 



and regularly imbricated. Upper arm plates fan-shaped and symmetrical. 



A few disk spines. One mouth papilla, . 

 Differs from preceding in disk scales less overlapping ; two mouth papiUse on I 



each side, and side mouth shields not meeting without, ... J 

 Six arms ; two mouth papillee on each side. Radial shields proportionately \ 



larger than in Ophiactis halli, upper and imder arm plates longer, and > Ophiactis loricata. 



disk scales less regular. Side mouth shields not meeting without (young?) ' 



Differs from Ophiactis halli in under arm plates, from loricata in fan shaped t ^ , . .. , 



^ > Ophiactis lymani. 



upper arm plates, . . . . . . ■ i 



Near Ophiactis halli, but only three arm spines; no disk spines. Teeth lobed. 

 Side mouth shields not meeting without, ..... 



Disk scales distinct and naked, without spines. Three stout, blunt, tapering, 

 cylindrical arm spines. One large fiat mouth papiUa on each side. Teeth 

 lobed. Five arms, 



Dtfi'ers from Ophiactis halli in arched disk with radial shields not well dis- 

 tinguished from other scales ; and in transverse ov.al upper arm plates, 



i Ophiactis plana. 



Ophiactis flexuosa. 

 \ Opln 



>hiactis virens. 



