AMPIIIURA ATRA. 127 



Amphiura atra Lutkex. 



Ophiolepis (itra Stimi'SOX. Phk-i-imI. Boston Soc. \,it. Hist., IV. ]>. 225. 1852. 

 Amphiura (Ophiolepis) aim Lutkk.n. Addit. ad Hist. Oj)!!., p. US. 



Special Jlarlix. — Throe arm-spines ; under arm-plates narrower with- 

 out than within, their outer side re-enteringly curved ; moutli-papilhu 

 malving a connected hue ; inuermo.st pair running upwards to the teeth. 



Descrijjtion of a Specimen. — Diameter of disk, 9.5"""" ; from outer 

 side of mouth-shield to outer corner of opposite mouth-slit, 3.G'"'"" ; 

 width of arm without spines, 2"""- ; length of arm about 95"""" ; dis- 

 tance from outer side of mouth-shield to inner points of mouth-pa]Mlhv, 

 to that between outer corners of mouth-slits, 1.6 : 1.6. Moutli-papilla3 

 wide, somewhat angular, applied end to end, so as to form a connected 

 line ; innermost pair extending upwards towards the teeth, and thus 

 partly holding the place of tooth-papilhx? ; usually six, sometimes eight, 

 to each angle of the mouth. Teeth nine ; lowest one small, irregtdar, 

 often broken in two or three pieces ; the rest squarish, flattened, very 

 regular, increasing a little in size towards the upper ones. Mouth- 

 shields small, diamond-shape, longer than broad ; length to breadth, 1 :.6 ; 

 madreporic shield larger and swollen. Side mouth-shields comparatively 

 large, meeting Avithin, broader without than within, and with a slight 

 curve like an S. Under arm-plates broader than long, broader within 

 than without ; inner and lateral sides nearly straight, outer side re- 

 enteringly curved, corners rounded ; length to breadth (seventh plate), 

 .5 : .8 ; the plates are in contact only at the base of the arm ; about the 

 twelfth plate they begin to l^e separated by the side arm-plates, and 

 begin also to have a slight peak on their inner side, which is the point 

 of juncture of two slightly curved inner laterals ; the first plate is quite 

 rudimentary. Side arm-plates rather feeble, long, encroaching above 

 and below, having a very small ridge for spines. Upper arm-plates 

 much brcader than long, pointed oval, with outer side nearly straight, 

 and inner sides curved ; separated from each other except on the mid- 

 dle line ; length to breadth (tenth plate), .6 : 1.7. Disk with closely 

 overlapping scales, about 36 to a square mm. ; below finer ; near radial 

 shields larger ; from near the outside corner of the radial shields runs a 

 single straight row of larger scales, passing diagonally over the edge 

 of the disk. Radial shields rather large, irregular oval, with a point 

 Avithin, united without, within separated by a group of scales ; length to 

 breadth, 2 : .9. Arm-spines short, round, tapering, sharp ; lengths of two 

 lower ones to that of under arm-plate, near base of arm, .9, .9 : .5 ; upper 

 one somewhat shorter. Tentacle-scales two, broad, short, erect, with a 



