ECHINOIDEA. II. 



77 



The nearest relation of P. (Echinosigra) paradoxa is P. (Echinosigra) phlalc; it agrees with that 

 species in the main features of the test, as also in the pedicellarise and spines. That it is a distinct species 

 and not only representing the grown form of P. phialc is beyond donbt, as is easily seen by a direct 

 comparison of the largest specimen of phialc (ij mm ) with the smallest specimen of paradoxa (22 mm }\ both 

 these specimens show all the characteristics of their species quite distinctly developed --it would be 

 quite unreasonable to think that a form like that figured in PI. VI. Figs, i 2, 7 (phialc) could be trans- 

 formed into a form like that figured in PL VI. Figs. 17, 19, 21 (paradoxa) during the growth from a 

 length of 17""" to a length of 22""". The fact alone that in the specimen of phiale of i7 mm the lowest 

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

 3'5 mm high, is sufficient to prove them to be two distinct species. 



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

 less quiet regions it would run the risk of breaking the neck. L/oven (On Pourtalesia. p. 85) thinks 

 that several of the more important characters of the Pourtalesise point though remotely, towards 

 animal forms of another and higher type, animals of annulose differentiation >. Had be known the 

 species here described, he would probably have seen a confirmation of this view herein, except as 

 regards the annulose differentiation >, of which there is no trace. One might easily fancy how such a 

 form, if it proved favourable in the struggle for life and the species therefore became numerous and 

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

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

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



I may here give some additional information, mainly on the pedicellarise of the other species 

 of Pourtalesise which I have had occasion to examine in the British Museum. 



Pourtalesia carinata A. Ag. Regarding the structure of the test of this species I may refer to 

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

 the labrum are not a double sternum, as it is interpreted by L,oven, but the ambulacral plates 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 Museum, unfortunately, does not allow one to state this by direct observation, no 

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

 Report are given several figures of the pedicellarise, which in the explanation of plates 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 pedicellarise in this species, viz. 

 globiferous, rostrate and tridentate. The globiferous pedicellarise (PI. XL Figs. 16, 22) have the valves 

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

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

 evidently glandular skin; there is no neck; the stalk is rather compact. The rostrate pedicellarise 

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

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

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

 The tridentate pedicellarise are richly developed; in the larger forms there is a very long tooth at the 

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



