﻿OnilOCERAMIS JANUARII. 63 



lapping the second, which is the largest of all ; the space below the 

 tooth-papilloe is commonly vacant, but is sometimes occupied by two 

 very small mouth-papillai. Tooth-papilla3 two ; narrow, long, and a 

 little curved, touching each other below, but diverging upwards, leaving 

 a triangular space, which is filled by the lowest tooth.* Teeth ten, 

 flattened, squarish, with a wavy cutting edge, which is re-enteringly 

 curved, and thickened at its middle point ; lowest one more or less 

 modified by the two tooth-papillEe ; the next four of even width, and 

 broader than the five uppermost ones. Mouth-shields rounded, about 

 as long as broad, with a curve within and a rounded angle without ; 

 length to breadth, 1.8 : 1.6. Side mouth-shields irregular, and very 

 small. Under arm-plates much broader than long, broader without 

 than within ; outer and inner sides curved ; lateral sides strongly re- 

 enteringly curved ; outer corners prolonged laterally, as little peaks ; 

 length to breadth (eighth plate), 1.1 : 2.2 ; first plate very small, 

 rounded diamond-shape ; breadth 1""" ; towards the end of the arm the 

 plates become proportionately much longer, but the curves of their 

 sides remain about the same. Side arm-plates not encroaching above 

 or below ; considerably thickened along their outer edge, to afford a 

 base for the strong arm-spines. Upper arm-plates much broader than 

 long ; broader without than within, with outer comers well rounded ; 

 they are divided on the middle line into two quite distinct pieces, very 

 rarely into three or even four pieces ; the two or three first plates are 

 short and rudimentary, and are enclosed by the notch in the disk. Disk- 

 scales closely overlapping ; in the centre a circular, primary plate, 

 about 1.5"""' in diameter ; four primary plates may be indistinctly seen 

 in each interbrachial, and three in each brachial space ; on the inter- 

 brachial spaces below, the scales are narrow, close, small, and even, 

 having an average length of about .T""' ; at the base of each arm, 

 there are very fine scales, which often run out a little way on the side 

 of the ann, much as in Ophiura. Arm-spines three (near base of arm, 

 sometimes four), stout, strongly tapering, rounded, a good deal flat^ 

 tened ; middle one longest ; lengths to that of under arm-plate (thir- 

 teenth joint), 1.7, 2.5, 2 : 1.1 ; the upper spine often is suddenly enlarged 

 at the base. Tentacle-scales small, rounded, flattened, a little longer 

 than broad, standing close together ; near the base of the arm there are 

 two outside and two inside each pore ; but farther out the two outer 

 ones become smaller and smaller, and are soon reduced to a little edge, 

 lying along the lateral side of the under arm-plate. Color, in alcohol : 

 yellowish vandyke-brown, above ; below, the same, but lighter and more 

 yellowish. 



* These might almost as well be termed mouth-papilla;, except that they do not lie quite on a 

 level with the rest. The innermost papillse in Amphiura are similar, but descend, so as to form 

 part of the row of mouth-papillae, among which they are included. 



