Th. Mortensen: On the allegcd primitive Ophiuroid, Ophioteresia degatu Bell. 



15 



In the simply dried specimens a series of somewhat heart-shaped piates, with a 

 slight median furrow, is seen on the ventral side of the arms (PI. 1. Fig. 11). On 

 dissolving the skin one finds them to be polygonal piates, which, however, do not 

 represent the ventrai piates alene. The ventral piates are so closely attached to 

 the vertebræ that their limits cannot be distinguished, and it is only when they 

 are loosened by the prolonged action of the dissolving fluid that their real 

 shape can be observed. They are then found to have a rather peculiar shape, 

 (PI. I. Fig. 13) being elongated, with a pair of wing-like expansions near the distal 

 edge; in the middle line is a slight furrow, bordered by a slight elevation on each 

 side, forming a distinct keel on the inner side. The ventral plate does not cover 

 more than the median part of the ventral side of the vertebra. The first ventral 

 plate has a somewhat different shape (textfig. 3) ; its inner 

 half is bent inwards, being at an angle with the outer part 

 (the Hne across the middle of the plate in textfig. 3 is the 

 hmit between the outer and inner part of the plate, but the 

 plate is not divided). The dorsal side of the arm is covered 

 by a number of small, irregular piates, among which no 

 primary dorsal plate can be distinguished ; they may, how- 

 ever, be much more grain-like than in the specimen figured. 

 On the young joints near the point of the arm there is only 

 one, median, dorsal plate. The side arm-plates are very 

 prominent, as seen especially when the skin has been rc- 

 moved (textfig. 3). They do not widen at their base, so that 

 a conspicuous nakcd space is left between them. The arm 

 spines are 5 — 6 on the inner joints. They are rather slendcr, 

 but on a microscopical examination are casily seen to be 

 transformed hooks. The tube feet, which are closely covered 

 with sensory papillæ, as in Ophiolhrix a. o., issue from the 

 sides of the arm, but on the inner joint they occupy the position 

 usuui in Ophiurids. No tentacle papillæ are found, cxcept on the young joints near 

 the point of the arm, where a rudimentary papilla is observed as in Ophioteresis. 



The colour is, in the preservcd specimens, white or light reddish ; on the dorsal 

 »ide of the arms there is on every S — 4 joints a pair of conspicuous black bands 

 arrosH the arm ; also on the radial shields there may be dark spots. Sometimes 

 the dark bands on the arms are rcpresented only by small black spots. 



The vertebræ are very nearly of the same shape as thosc of Ophioteresis. Also 

 the glassy grains on their dorsal side are well developed. 



Textngure 3. 

 Inner part of an arm of 

 Ophiothda vineuUi, tri'atcd 

 with Eau de Javellc, 

 whcrcby the limits of 

 the piates have been 

 made distinct. The arm- 

 spincs have liocn omit- 

 ted. "/i 



