﻿74 OPHIOCOMA ALEXANDRI. 



Ophiocoma Alexandri Lyman. 



Ophiocoma Alexandri Lyman. Proceed. Boston Soe. Nat. Hist., VII. p. 256. 18G0. 



Sjjecial Marks. — Grayish or yellowish brown. Arms Ijanded ; five 

 to seven spines ; third or fourth spine longest. 



Descri2Jtion of a Sjjecimen. — Diameter of disk, 17™™- ; from outer 

 side of mouth-.shield to outer corner of opposite mouth-.slit, 5.5™™' ; width 

 of arm without spines, 3.3"™' ; length of arm, 120™™' ; distance from outer 

 side of mouth-shield to inner points of tooth-papillEe, to that between 

 outer corners of mouth-slits, 2.7 : 3. Mouth-papillas flat, rounded, of 

 nearly equal size, rather small ; nine or ten to each angle of mouth. 

 Tooth-papillte bead-like, crowded, most of them in two vertical rows ; 

 about nine in number, the upper middle one larger than the others. 

 Teeth three or four, stout, flat, a little tapering. Mouth-shields nearly 

 round, with inner end slightly truncated ; length to breadth, 1.6 : 1.6. 

 Side mouth-shields very narrow and small, occupying the inner part of 

 mouth-shield, but not meeting within. Under arm-plates very regular, 

 not overlajiping, rounded octagonal, inner angles less rounded than 

 outer ; the plates within the disk a good deal smaller than those 

 beyond ; length to breadth (twentieth plate), 1.2 : 1. Side arm-plates 

 encroaching somewhat above. Upper arm-plates regular ; oval heart- 

 sliajDe, with the point inward ; outer corners very cleanly curved, outer 

 side nearly straight; length to breadth (ninth plate), 1.2:2.2. Near 

 tip of arm, the plates are regular heart-shape, with an acute point 

 turned inward. Grains of disk elongated so as to form short spines, 

 like grains of wheat, of different sizes ; about 25 to a square mm. ; of 

 the same character below, but less numerous ; a bare strip running 

 along edges of genital slits. Arm-spines five, robust, rounded, somewhat 

 flattened, a little tapering, blunt ; the longer ones sometimes bent ; 

 third spine from the toji longest ; the longest sjDines are near the 

 twentieth joint; lengths to that of under arm-plate (eighteenth joint), 

 2, 2.2, 2.7, 1.8, 1.5 : 1.2 ; tAvo lowest spines more slender than the upper 

 ones. Sometimes a short supplementary spine above. Longest spine 

 on this specimen, 3.2™™-. There are five spines to each joint till close 

 to the tip of the arm, where there are only four. Close to the disk 

 there are commonly six spines, which, however, are a good deal smaller 

 and more even than those beyond. Tentacle-scales large, rounded oval, 

 length to that of under arm-plate, .5 : 1.2 ; on first two or three joints 

 two, on all the rest only one. Color, in alcohol : above, disk uniform 

 gray-brown (Cologne earth and neutral tint) ; arm-spines and ujiper 

 arm-plates light yellowish-brown ; the former darker at their base ; 



