ECHINOIDEA. II. 



73 



importance for tlie animal, since it is liardly conceivable, how the animal conkl i^ci the rij^liv position 

 again, if it were turned over, the short spines heiuL^ hardly able to set up the thick body with its 

 heavy contents. In the younger specimens the \'enti al side is not so flat, but the spines are here com- 

 paratively larger and in so far better adapted for keeping the body in the right ])osition. 



Some measurements are given here of tlie three best preserved sjK-cimens; the two larger ones 

 have only a few small holes in the test; in the third one the neck is broken, but the specimen is 

 otherwise well preserved. The other specimens are represented b\- separated anterior and posterior 

 end.s. — All the measurements are in nnn. 



Total length Width of head Width of neck > Height of Mieck Height of > body Width of body • I,ength of Uail-. 

 37 fa 3 5 125 12 4 



26 47 2-5 3-S S 5-S 3-5 



22 4S 3 3'5 75 6 3-5 



The structure of the test (PI. VI. Fig.s. 17, 19, 21. PI. \'II. F'ig- 5) is e.s.sentially the .same as in 

 P. pliiale. the main difference lies in the extreme elongation of the inner plates of the bivium. The 

 labrum is rather broad and very long, 6-5"'™ in the specimen of 26""" length. The inner ])lates of the 

 ambulacra I and \' are both well developed, narrow atid very elongate, joining at their outer end 

 the second plate of the corresponding series, the bivial ambttlacra thus being uninterrupted. Each of 

 the inner plates carries a single tube-foot', the same is the case in the ambulacra II and I\', the 

 edge of the invagination thus being provided with 8 rather well developed and distinct tube-feet. The 

 plates I. a, II. a, IV. a V. b thus do not carry two jjores, but their relative size is in conformity 

 with the general rule. The inner plate of the interambulacra i and 4 is distinct, but, as in pJiialc, 

 separated from the corresponding second plates by the widened ambulacral plates II. a. 2—3 and IV. 

 b. 2 — 4. The labrum joins at its outer end the two ambulacral plates I. a. 2 and \'. b. 2. They are also 

 very much prolonged, no less than /'S'"™ in the specimen of 26'""' length, somewhat widened in the outer 

 half. As in phialr they show the curious feature of being split up at the oral and aboral end by a 

 longitudinal line proceeding from both ends a long way into the plates; these two lines, however, do 

 not join in the middle (PI. VI. Fig. 21), the plates thus being undivided. In this figure the outer part 

 of the oral end of this plate is seen to be prolonged a considerable distance along the labrum to meet 

 the first ambulacral plate; in the largest specimen it is — as far as I am able to discern it — not pro- 

 longed orally down the side of the labrum, in the smaller one it is somewhat prolonged, but not so 

 much as in the specimen figured here. The sternum is situated very far back; it is not so nuich pro- 

 longed, 5™'" long in the specimen figured; the episternal plates which are comparatively rather short 

 (3™"'), reach the point of the anal snout. The epiproctal plates are three on eacli side, viz. 5. a. 6 — 8 and 

 b. 7—9. The abactinal plates of the odd interambulacrum are not distinctly prolonged, their number 

 therefore being larger than usual, 15 or 16 in the specimen figured of 26""" length. The bi\-ial ambu- 

 lacra begin on the abactinal side at the anterior end of the test, being thus very little separated from 

 tho.se of the trivium, which occupy the usual position at the anterior end of the test. The posterior 

 paired interambulacra (i and 4) are very curiously modified (F'ig. 13). The plates a. 2 and b. 2 are 



1 In V. a there is exceptionally no pore in the .specimen figured (PI. V. Fig. 2i). 

 The Injjolf-Fxpedilion. IV. i. lO 



