ECHINOIDEA. II. 77 



The nearest relation of P. (Echinosigra) paradoxa is P. (Echiiiosigra} pliialc; it agrees with tliat 

 species in the main featnres of the test, as also in the pedicellariæ and spines. Tliat it is a distinct species 

 and not only representing the grown form of /'. phialc is be\ond donbt, as is easih' seen by a direct 

 comparison of tlie largest specimen oi />///a/c [ly'""') witli the smallest specimen of/^^/v/ (/c/ a'« (22"""); Ijoth 

 these specimens show all the characteristics of their sjjecies qnite distinctly developed — it wonld be 

 qiiite unreasonable to think that a form like tliat fignred in PI. VI. Figs. i — 2, 7 (phialc) conld be trans- 

 formed into a form like that fignred in PL VI. Figs. 17, 19, 21 (paradoxa) dnring the grovvth from a 

 length of 17""" to a length of 22'""'. The faet alone that in the specimen oi pliialc of 17""" the lowest 

 part of the anterior end is 5""" high, whereas in the specimen of paradoxa of 22""" the neck is only 

 3-5""" high, is snfficient to prove theni to be two distinct species. 



A form like this species is, evidently, only fit to inhabit the soft bottoni of the deep sea; in 

 less quiet regions it wonld rnn the risk of breaking the neck. Loven (On Ponrtalesia. p. 85) thinks 

 that several of the more important characters of the Ponrtalesiæ point thongh remoteh', towards 

 animal forms of another and high er tyjse, animals of annnlose differentiation . Had be known the 

 species here described, he wonld probably hav'e seen a confirmation of this view herein, except as 

 regards the annnlose differentiation , of which there is no trace. One might easih- fanc\' how snch a 

 form, if it proved favonrable in the strnggle for life and the species therefore became numerons and 

 wide spread, might give rise to qnite new types, in which the Echinoid organization would scarcely 

 be recognizable. — It is, however, more probable that this form represents an extrenie development, 

 the nltimate end of that branch of the great Echinoid genealogical tree. 



I may here give some additional information, mainly on the pedicellariæ of the otlier species 

 of Ponrtalesiæ which I have had occasion to examine in the British Mnsenm. 



Ponrtalesia carinata A. Ag. Regarding the strnctnre of the test of this species I may refer to 

 the remarks above (p. 71), in which I think it is shown beyond donbt that the two piates following 

 the labrnm are not a double sternnm, as it is interpreted by Loven, bnt the ambulacral piates I. a. 2 

 and V. b. 2, the species thus agreeing with P. phialc and paradoxa in this respect. The material pre- 

 served in the British Mnsenm, unfortnnately, does not allow one to state this by direct observation, no 

 specimen having more of the plastron left than what has been fignred by Loven. In the ■ Challenger 

 Report are given several figures of the pedicellariæ, which in the explanation of piates are named: 

 large-headed , hooked pedicellaria, large-based, slender-pronged and Clypeastroid-like pedicellaria. In 

 the description they are not mentioned. I have found three kinds of pedicellariæ in this species, viz. 

 globiferons, rostrate and tridentate. The globiferous pedicellariæ (PI. XI. Figs. 16, 22I have the valves 

 ending in two (.sometimes three) rather large teeth; it is this form which is fignred in the Challenger ■ 

 Report PI. XL\'. Fig. 49, as a large-based, slender-pronged valve ■. The head is invested in a thick, 

 evidently glandnlar skin; there is no neck; the stalk is rather compact. The rostrate pedicellariæ 

 (PI. XI. Fig. 39) are of a peculiar form; the ba.sal part of the valves is very broad, with finely serrate 

 edges; the narrow blade is short and thick, with the onter edge ronnded, not forming an angle with 

 the; side-edges; it is rather coarsely serrate, the teeth continning a little way down the side-edges. 

 The tridentate pedicellariæ are richly developed; in the larger forms there is a ver\' long tooth at the 

 point, in smaller ones this tooth is less prominent, or not at all differing in size from the teeth along 



