NEW FEATURES US PELAXECHIXTTS COEALLIXTJS. 



709 



in the "Woodwardian Museum are given in fig. 4. At one place the 

 peristomial plates are beautifully preserved ; here a row of at least 

 13 plates is visible, on each of which (except the most adoral, which 

 is partially hidden) a pair of pores is seen *. These, as Keeping 

 points out, are arranged approximately in a vertical row. Each plate 

 extends from the median ambulacral to the median interambulacral 

 line. This is also seen more or less clearly at other points, both in 

 the Woodwardian and my own specimen. There are thus 10 rows of 

 imbricating plates, and all are perforated by pores. The arrange- 

 ment thus differs from that in Cidaris, where imbricating plates de- 

 void of pores are found opposite the interambulacral area, but is 

 identical with that found in Asthenosoma Grubei f , Phormosoma bur- 

 saria t, Phormosoma Juculenta §, &c. The overlapping plates much 

 resemble those of Asthenosoma hystrix\\ and of Phormosoma bursaria^ 

 and they imbricate and overlap one another in exactly the same way. 

 The inferior (oral) edge of most of the plates is tolerably straight, 

 but in those nearest the mouth it is raised up into an eminence 

 which supports a member of one of the three rows of tubercles with 

 which these plates are provided. 



Pedicellarice (PI. XXYIII.). — A feature of great interest is the 

 occurrence of the structures known as pedicellarige. These, which 

 were first made known by 0. F. Miiller**, and have been variously 

 looked on as parasites, young stages of Echini, &c, are now 

 recognized as spines peculiarly modified for prehensile purposes. 



They have not hitherto, so far as I have been able to ascertain, 

 been described as occurring in a fossil state. Prof. Zittel remarks 

 in his ' Handbuch der Palaontologie,' vol. i. p. 474 :- " Pedicellarice 

 .... are of no practical significance to the palaeontologist, since, 

 on account of their delicate nature and small size, they are not 

 capable of being preserved." I have, however, found them in great 

 variety and abundance, and in beautiful preservation. 



Though small, they are distinctly visible to the naked eye. The 

 only satisfactory way to examine them was, I found, to place the 

 whole urchin on the stage of the compound microscope, and use a 

 good illumination. If this method were employed, I believe the 

 pedicellariae would be found in many other cases also. 



The pedicellariee of Pelanechinus are all 3-valved, and their surface 

 shows here and there numerous granulations. I have found three 

 distinct varieties, and of the three kinds into which the pedicellarige 

 of Echinus were divided by Yalentinft, whose nomenclature has 

 been generally adopted, I believe two are represented. 



* Prof. Zittel, in his ' Handbuch der Palaontologie,' vol. i. p. 504, refers to this 

 form as having, according to Keeping, peristomial plates devoid of pores ; this, 

 however, is not correct, as Keeping distinctly states that the ambulacral pores 

 are continued over these plates to the mouth. They are also visible in my spe- 

 cimen ; but fig. 3 will remove all doubt. 



t ' Challenger ' Eeport, Echinoidea, pi. xvii. figs. 1-4. 



+ Ibid. pi. xb. fig. 3. § Ibid. pi. x«. fig. 4. 



|| Phil. Trans. Royal Soc. 1874, pi. lxvi. fig. 1. 



^[ ' Challenger ' Eeport, Echinoidea, pi. x b. fig. 3. 

 ** Zoologia Danica, 1788, p. 16. tt Monographic de l'Echmus. 



