PALEOPNEDSTES CIUSTATQS. 59 



al the extremity of the petaloid ambulacra or the petals themselves, as in 

 one of ili" species of Rhinobrissus, bul crossing them below the petals at 

 an indefinite place of the tesl ; so thai we mighl have an interior fasciole, 

 in Lovenia; a true peripetalous fasciole, as in Hemiaster; a transpetaloid 

 fasciole, as in Gualteria and Rhinobrissus; or a marginal fasciole, as in some 

 Btages of growth of Paleopneustes and in Linopueustes ; all representing 

 differenl stages of developmenl or modification of a petaloid fasciole. This 

 simple scries becomes complicated with the possible simultaneous existence 

 of an internal and peripetalous fasciole or of a true peripetalous fasciole 

 with a more or less marginal fasciole, forming in thai case a lateral fasciole 

 proper. In a specimen of this species measuring aboul 85 mm. in length, 

 the marginal fasciole is traced only with difficulty near the ambitus across 

 the anterior lateral ambulacra (PI. XXI. Fig. 8), and it seems to disappear 

 Completely in Bomewhal older specimens. Bui in all the stages of growth 

 thai pari of the ambitus and of the tesl adjoining the course of the mar- 

 ginal fasciole is thickly studded with miliaries and small secondary tubercles 

 (PI. XXI. Figs. -2. 6, 8). 



In Linopneustes this marginal fasciole has assumed practically all the 

 characters of a peripetalous fasciole crossing the posterior lateral ambulacra 

 justal the end of the petals, while it still crosses the anterior ambulacra a 

 shorl distance below the end of the petals. Neither in Paleopneustes cist,, his 

 nor in P.hystria do we find an\ trace of a rudimentary subanal fasciole. either 

 as an indistinct hand or a pari of a hand, or even as accumulations of miliary 

 tubercles; and it is interesting to note that in species so closely allied as 

 /' cristaius and Linopneustes Wurrayi there should he so striking a distin- 

 guishing feature as the presence or absence of a subanal fasciole. while 

 in other genera of Spatangoids, Palaeotropus, Urechinus, and Schizaster, in 

 specimens of the same species, -iich a- / reclaims naresianus, we should have a 

 complete series passing from a well-defined subanal fasciole to a mere accu- 

 mulation of miliary tubercles. 



The smallest specimen collected, measuring aboul 16 mm. in length, is 

 somewhal more flattened than the older Btages, and Bhows as yel no trace oi 

 petals, the ambulacral plates and pores extending uniformly from the apex 

 to the ambitus and actinostome without the specialization of any portion. 

 (PI. XXI. Figs. 9-11.) In this stage I could see no indication of a marginal 

 fasciole. The apex was compact, hut there was no trace a- yel of any 

 genital openings, and. the madreporic body was very faintly indicated (PI. 



