10 

 II. Wissenschaftliche Mittheilungen. 



1. Astrophiura per m ira. an Echinoderm intermediate between 

 Ophiuroidea & Asteroidea. 



By W. Percy Sladen (of Halifax, England). 



A notice appeared in the »Zoologischer Anzeiger« for Nov. 25., 

 (No. 13) , of an abstract of a paper »On Astrophiura permira, an Echino- 

 derm-form intermediate between Ophiuroidea and Asteroidea«, (Proc. 

 Roy. Soc. No. 188). Several queries having subsequently been ad- 

 dressed to the author by continental Naturalists, a short summary of 

 the characters of the organism in question may not be unacceptable, 

 pending the publication of the details in full. 



The test, which is pentagonal in form and depressed, is covered with 

 plates which, on the central half of the abactinal surface, are arranged 

 after the manner of an ophiuroid disk , whilst these of the outer portion 

 of the pentagon represent very highly developed modifications of 

 brachial plates. In other words there occurs in this Echinoderm a 

 combination of the disk- and arm-structure of an ophiuran consolidated 

 within an asteroid form of body. 



Extending from the angles of the disk, and in continuation of the 

 radial series, is a very short and aborted rudimentary ray of ophiuroid 

 type; but which, both in size and character, is quite insignificant in pro- 

 portion to the dimensions of the disk. The margin of the test is sur- 

 rounded with a close-set fringe of small compressed spinelets. 



On the actinal side, the mouth is central and surrounded by ten 

 large mouth-plates which bear papillae only; teeth, jaw-plates and 

 jaws wanting; one mouth-shield present. The entire armature being 

 more asteroid than ophiuroid in general facies. 



The ambulacral system is quite asteroid in character ; the tentacles 

 being retractile (in all probability perfectly), and the divisional plates 

 which separate them are not only homologous with, but resemble in 

 the manner of their disposition, the ambulacral plates of Asteroidea. 

 Although a series of large quadrate plates which proceed along the 

 median line of the rays give at first sight a superficial resemblance to 

 the under arm-plates of Ophiurans, these in reality correspond with the 

 median plates which are present in the early stages of growth of an 

 Asteroid and are afterwards resorJbed in the process of the development 

 of the mature form. A transverse section through a radius likewise 

 confirms this blending of the characters of the two groups, for the ab- 

 normal arm-skeleton, which is present, is of a type modified to accord 

 with the asteroid characters above noted. In fact, the whole series of 

 radial plates, when studied from the actinostome to the extremity of 



