4o 



ECHINOIDEA. II. 



Eig. 3. Ureckinus naresianas. 



Peristome and adjoining part 



from the inside. '- 1. 



succeeded in making clear the limits of the plates, either by treating it with alcohol-glycerine, mount- 

 ing it in Canada balsam or drying it. The most prominent feature of the specimen is the position of 

 the anal area, almost iii the middle of the abactinal side. The subanal fasciole is faintly indicated; 



the spines are rather long, equalling in length the diameter of the test. 

 The pedicellaria; are like those of the adult specimens, viz. the globiferous 

 and small ophicephalous (see below), other kinds not being found. The 

 peristomial tubefeet are already penicillate. 



The next size represented is yz ) mm in length. Here the anal area 

 has reached near to the posterior end of the test, three pairs of plates 

 being developed above it in the unpaired interambulacrum ; the ventral 

 side, however, projects still a little beyond the anal area, the posterior 

 end of the test thus sloping a little downwards and outwards, whereas in 

 later stages it is vertically cut, and in grown specimens the posterior end 

 slopes downwards and inwards, the abactinal side projecting over the anal 

 area, till at last the anal area is almost on the flat actinal side. The fi- 

 gure 4 shows the position of the anal area in the different stages. — The plastron and bivium in 

 this specimen of j-^ mm has upon the whole the same form and relations as in the grown specimens. 

 The subanal fasciole is distinctly developed. The apical system is essentially as in the grown 



specimens. — In the next stages I find no important changes to 

 notice. Thev become °fraduallv hi°;her, however, there is a rather 

 great variation in the height in grown specimens, as remarked by 

 Agassi z. The displacement of the periproct gives the most promi- 

 nent change. The genital openings appear rather late ; I have not 

 seen them in specimens smaller than 22 mm , but sometimes they do 

 not develop till later, thus there is no trace of them in a specimen 

 of 2j mm . The genital pores (three in all the specimens) are covered 

 by very conspicuous genital papillae. - ■ It may be noticed that the 

 plates show the same marks of growth and radiating ridges as de- 

 scribed and figured from Cystechinus Wyvillii by Agassiz (Chall.- 

 Ech. PI. XXIX. b. 9), though not so distinct as in that species; the 

 same feature has been made known for the fossil Echinocorys ciply- 

 ciisis by Lambert 1 . 



The primary spines (PL IX. Fig. 30) are very slender, the 

 longest ones found are ca. 5 mm ; they are almost all broken on all 

 the specimens except the smallest, in which they are as long as the 

 diameter of the test. They are smooth in the lower part, somewhat 

 spinous in the outer part, terminating in a short, oblique thorn. Those of 

 the actinal plastron are, judging from the very few unbroken ones found, a little flattened at the point, but 

 not widened. The clavulse of the fasciole are like the miliary spines (PI. IX. Fig. 31) covering the ab- 



CD 



7. .>" m m 



/J mm 



Fig. 4. Outlines in profil of different 

 stages of Urechinus naresianus, show- 

 ing the change in the position of the 

 anal system. 



1 Etude nionographique sur le genre Echinocorys. (Mem. Mus. R. d'hist. nat. de Belgique. II. 1903. p. 28. 



