176 



ECHINOIDEA. I. 



- Tetradactylous pedicellariae I have not found. The tridentate and triphyllous pedicellariae as iif 

 fenestratum; the large form of tridentate pedicellarise is found in very different sizes, but also the 

 small ones are of the typical structure, so that they cannot be confounded with the other form. 

 Besides the forms of the second kind of tridentate pedicellarise mentioned and figured for fenestratum, 

 a form is also found here where the blade is not at all involved below (Fig. 10). I have, however, 

 once found this form in A. fenestratum (in a specimen from Barbados, in British Museum), and so it 

 can be no specific character. The spicules, perhaps, are a little smaller than in fenestratum, but this 

 difference is too little marked to be used as a specific character. The best character is the colour, 

 which in the preserved specimens is deeply dark violet, while all the specimens of fenestratttm I have 

 seen, are quite bleached in alcohol: also in the living animals the colour is quite different com p. 

 the description by Wyv. Thomson. The primary spines on the actinal side are dark with a rather 



large, white hoof, very conspicuous on the dark 

 ground-colour. - The organs of Stewart are very 

 large; the longitudinal muscles powerful. -- For 

 this species, the place of which is evidently 

 between A. fenestratum and coriaccum, I propose 

 the name of Araeosoma violaceum n. sp. 



Echinosoma uranus (p. 57). A couple of speci- 

 mens of this species (Talismam Sahara, 938 m.) 

 I have seen in the museum of Paris. All the 

 primary spines on the actinal side were broken, 

 but some of the spines round the mouth had a 

 little hoof; after this there can be no doubt that 

 the primary spines on the actinal side end in a 

 hoof as in E. tenue. The large tridentate pedicel- 

 larise are quite similar to the one of E tcnitr 

 figured on PI. XII. Fig. 35, with the exception that 

 here the apophysis does not continue into the 

 blade as a crest. 



Hygrosoma Petersii (p. 59). In a specimen of this species (the Azores, 1258 m. Talisman . 

 The museum of Paris) was found a pedicellaria (Fig. n) forming a transition between the ophicephal- 

 ous pedicellarise in Tromikosoma Koehleri and the short, thick pedicellariae of // luculcntum. After 

 this there can be -no doubt that luculentum is really to be classed together with H. Petersii, and it 

 may well be supposed that this form of pedicellarise will also be found in //. hoplacantha -- in other 

 words that it is one of the characters of the genus Hygrosoma. Whether it is then to be regarded as 

 an ophicephalous or a transformed tridentate pedicellaria is so far of no consequence; I think it, 

 however, most correct to regard it as an ophicephalous one, although in luculentum it is not of the 

 typical structure. - The form of pedicellarise in H. luculentum (Chall. PI. XLIV. Fig. 27) mentioned on 

 p. 60, I have not been able to find by a renewed examination of the specimen from st. 200, although 

 this specimen is rather well preserved. -- If thus ophicephalous pedicellarise are found in the genus 



Fig. 10. 



Fig. ii. 



Fig. 10. Valve of tridentate pedicellaria of Araosoma violaceum. 



Obj. A A. Oc. II. (Zeiss). 

 Fig. ii. Valve of ophicephalous pedicellaria of Hygrosoma 



Petersii. Obj. A A. Oc. I. (Zeiss). 



