i 



164 



THE OPIIIURIDiE. 



founded.) In 0. Semoni only tlie arm-plates and the middle of the mouth 

 shield is micovered ; in 0. nuda the whole mouth region and the radial 

 shields are uncovered, besides the arms. The small scales along the radial 

 shields recall those of other species of Ophioncreis. The covering of the disk 

 evidently is very variable in this genus, the species forming a series from the 

 rather coarse-scaled O.fusca Brock, through such forms as 0. reticulata Ltk. 

 and 0. nuda to 0, Semoni, 



43. OpMochiton carinatus n. sp 



Plate XIV. llffs. 1-3 



r 



Diameter of disk, 13 mm. ; width of arm close to disk, 2.8 mm. ; length 

 of arm, about 10-11 times the diameter of the disk. Five or six rather 

 long, conical mouth papilla) on each side, the outermost but one much larger 



than the rest ; one conical at the apex. Mouth angles rather long. 



Mouth 



Dor- 



shield wider than long, with an obtuse rounded angle within, inner sides 

 slightly, outer sides much re-enteringly curved; corners and outer edge 

 rounded'. Side mouth shields very narrow, not meeting within ; their outer 



end is a little widened. 



First ventral plate very small, six-sided. Those beyond wider than long, 

 rather broadly in contact to the end of the arm. Inner angle truncated, 

 outer edge with a rounded median peak, re-enteringly curved towards each 

 side ; inner and outer laterals concave, outer corners produced. A very dis- 

 tinct sharp keel along the median line of the ventral plates, only disappear- 

 ing towards the end of the arm. Side arm-plates with spine-ridge not very 

 prominent, not meeting below, and above only at the end of the arm. 

 sal plates a little wider than long, four-sided ; the inner edge scarcely half 

 as broad as the outer, the former concave, the latter strongly curved (or 

 with a rounded peak) ; lateral sides straight, outer corners sharp. At the 

 base of the arm there are some quite rudimentary dorsal plates and many 

 very small scales besides. Dorsal side of the arm with an indistinct keel. 



Disk covered with very small, overlapping scales, among which the pri- 

 mary plates are conspicuous. In the interbrachial spaces there are some 

 larger scales along the margin, overlapping towards the radial shields. 

 These are scarcely half as long as the radius of the disk, and half as broad 

 as long ; their adradial edge is slightly, the abradial edge much curved ; a 

 rounded peak within, outer edge straight ; they are wholly sel^arated by 



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