40 



ECHINOIDEA. II. 



Kig. 3. Urechinus naresianus. 



Penstome and adjoining part 



frotn the inside. 2/,. 



succeeded in making clear the liniit.s of the piates, either b\- treatino; it with alcohol-ghcerine, mount- 

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

 the anal area, almost in the middle of the abactinal side. The snbanal fasciole is fainth- indicated; 



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

 The pedicellariæ are like those of the adnlt specimens, viz. the globiferons 

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

 peristomial tnbefeet are alread}- penicillate. 



The next size represented is 7-5""" in length. Here the anal area 



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



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 thns sloping a little downwards and ontwards, whereas in 



later stages it is vertically cnt, 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 po.sition 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 essentialh- as in the grown 



specimens. — In the next stages I find no iniportant 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 gi\-es the most promi- 

 nent change. The genital openings appear rather late; I 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 

 b\- very conspicuous genital papillæ. — It raa\- be noticed that the 

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

 scribed and figured from Cystcchinus 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 Echi)iocorys ciply- 

 ciisis by Lambert". 



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



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



the specimens except the smallest, in wliich thev are as long as the 



diameter of the test. The)- 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 ver\- few unbroken ones found, a little flattened at the point, but 



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



■ Etude mouographique sur le genre Écliinocorj-s. (Mém. Mub. R. d'hist. nat. de Belgique. II. 1903. p. 2S.] 



15mrn 



ZSmmy 



Fig. 4. Outlines in profil of different 



stages of Urechinus naresianus, show- 



ing the change in the po.sition of the 



anal system. 



