4° 



ECHINOIDEA. II. 



Fig. 3. Urechinus naresianus. 



Peristome and adjoining part 



from the inside. - i. 



succeeded in making clear the limits of tlie plates, either b)- treating it with alcohol-glycerine, monnt- 

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

 the anal area, almost in the middle of the abactiual side. The subanal fascicle is faintly indicated; 



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

 The pedicellaria; are Hke 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 ne.xt size represented is 7-5""" in length. Here the anal area 

 has reached near to the posterior end of the test, three jjairs 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 abactiual 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 7'5""" 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 ne.xt stages I find no important changes to 

 notice. The\" become gradually higher, however, there is a rather 

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

 Agassiz. The displacement of the periproct gives the most promi- 

 nent change. The genital openings appear rather late; 1 have not 

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

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

 of 27""". The genital pores (three in all the specimens) are covered 

 by very conspicuous genital papilla.'. — It mav be noticed that the 

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

 scribed and figured from Cystccliiniis Wyvillii \>\ Agassiz (Cliall.- 

 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- 

 ensis l)y Lambert '. 



Tlic primary spines (PI. IX. Fig. 30) are ver\- slender, the 



longest ones found :ire ca. 5'"'"; the\- are almost all broken on all 



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



diameter of the test. The\- are smooth in the lower j)art, somewhat 



spinous in the outer ])art, 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 clavulte of the fasciole are like the miliary spines (PI. IX. Fig. 31) covering the ab- 



' fitude mouographique sur le genre fichinocorj^s. (Mem. Mus. R. d'hist. nat. de lielgitiue. II. 1903. p. 2S.) 



T^.f m m' 



Fig. 4. Outlines in profil of different 

 stages of Urechinus naresianus, show- 

 ing the change in the position of tlie 

 anal system. 



