p. HERBERT CARPENTER. 



Let us begin by studying the principal structural variations 

 that are to be met with in the arrangement of the apical plates 

 on the disc of Ophiurids. The apical system of the following 

 species remains permanently in an early embryonic condition. 

 There are five radial primaries in close contact with one 

 another, and with the dorsocentral just as in the young 

 Amphiura or Hemipholis already mentioned. 



Hemipholis wallichi, Dune. 

 Ophioceramis clausa. 

 OpLioglyplia convexa. 



„ forbesi. 



„ sculpta. 



„ scutata. 



„ soli da. 



„ undata. 



Ophiomastus secundus. 



„ tegulitius. 



Ophiomusium luuare. 



„ liitkeni. 



„ pulchellum (PI. 



1, fig. 9). 



„ simplex. 



Ophiopliolis aculeata. 

 Ophiopyrgus saccharatus, Stud. 



„ wyville-thomsoni. 



Ophiotrochus panniculus. 

 Ophiura carnea. 

 „ stuwitzi. 



N.B. — In this and subsequent lists the names given in the 

 * " Challenger " Ophiuroidea ' have been used, except where an 

 author^s name is appended. 



The radials of the young Amphiura do not long remain in 

 contact with the dorsocentral. For by the time that two 

 adambulacral plates have appeared between them and the 

 terminals they are separated from the dorsocentral by the rudi- 

 mentary basal plates, while under-basals are developed very 

 shortly afterwards. (PI. I, fig. 12; 2,3). In Hemipholis 

 cordifera, however, and also in Ophiura sarsi,^ more than 

 a dozen arm-joints are formed before the radials lose their 

 " primary " character and become hardly distinguishable among 

 the small plates which cover the disc. Those ofOphioglypha 

 minuta (PI. I, fig. 8; 4) and Ophiozona marmorea," although 

 still large and prominent, are separated at their central ends 

 by minute interradial plates, the basals (3). In the follow- 



1 "Additamenta ad liistoriam Opbiuridarum," i. Vid. Selsk. Skrifter, 5te 

 Kaekke. ' Naturv. og. math. Afdeling,' 5te Bind., Tab. i, fig. 3 a. 



- " Report on the Ophiuroidea dredged by the ' Blake,' " ' Bull. Mus. Comp. 

 Zoo!.' vol. X, No. 6, PI. iii, tig. 11. 



