OPHIACTIS. 



105 



OPIIIACTIS LUTKEN. 

 Tvi'E OF THE Gexus, O. Krehsii. 



Disk circular, robust, closely covered with radial shields and overlap- 

 ping scales, the latter ])earing a greater or less number of small spines. 

 Teeth. No tooth-papilla\ A few (usually two or four) small, delicate 

 mouth-papilla? to each angle of the mouth, situated near the outer cor- 

 ner of tlie mouth-slit. Arm-spines arranged along the sides of the side 

 arm-plates. Two genital slits beginning outside the mouth-shields. 



GROUPING OF SPECIES HEREIN DESCRIBED. 



'■ Radial shields separated and ~\ 

 very small ; side mouth- 

 shields broad, and making 

 a continuous ring round 

 the mouth. 

 Five arms in the adult, Two mouth-papilhr, -j Mouth-shields much broad- " 



er than long ; arm-spines 



0. simplex. 



0. Kroyeri. 



Six arms in the adult, Four mouth-papilla^, 



smooth, tapering, differing 

 much in length, 

 Arm-spines very short, blunt, ) ^ Mulleri. 



rough ; nearly equal, ) 



A slight lobe on the outer ^ 0. Krehsii. 

 s side of the upper arm- >- 0. virescens. 

 ( plate, ) 0. sexradia. 



S 



Ophiactis simplex Lutken. 



OpMoIepis simplex Le Coxte. Proceed. Pliil. Acad., V. p. 318. Nov., 1851. 

 Ophiactis (Ophiolepis) simplex Lutken. Addit. ad Hist. Opb., p. 130. 

 Ophiactis Orstedii? Lutkex. Addit. ad Hist. Oph., p. 129. 

 Ophiactis arenosa? LIjtkex. Addit. ad Hist. Oph., p. 129. 



Special Marks. — Radial shields widely separated, and comparatively 

 small ; spines very numeious in the lower interbracliial spaces ; disk- 

 scales inclinino; to a circular form, rather regular. 



Description of a Specimen. — Diameter of disk, 4""° ; from outer side 

 of mouth-shield to outer corner of opposite mouth-slit, 1.7°"°- ; width of 

 arm without spines, 1.1"""- ; length of arm about 28'"'°- ; distance from 



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