176 



ECHINOIDEA. I. 



— Tetradactylous pedicellariae I have not found. The tridentate and triphyllous pedicellariae as in 

 fenestratum\ the large form of tridentate pedicellariae 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 pedicellariae 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 fenestratum I have 

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

 the description by Wvv. Thomson. The primary spines on the actiual 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 coriaceum, I propose 

 the name of Araeosoma violaceum n. sp. 



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

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

 I have seen in the museum of Paris. All the 

 primary spines on the actiual side were broken, 

 but some of the spines round the mouth had a 

 little hoof; after this there can be no doubt that 

 the primarv spines 011 the actiual side end in a 

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

 lariae are quite similar to the one of E tenue 

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

 here the apophysis does not continue into the 

 blade as a crest. 



Fig. 10. 



Fig. 11. 



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



Obj. AA. Oc. II. (Zeiss). 

 Fig. 11. Valve of ophicephalous pedicellaria of Hygrosoma 



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



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

 The museum of Paris) was found a pedicellaria (Fig. 11) forming a transition between the ophicephal- 

 ous pedicellariae in Tromikosoma Koehleri and the short, thick pedicellaria; of //. luculentum. After 

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

 may well be supposed that this form of pedicellaria; 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 110 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 pedicellariae in //. luculentum (Chall. PI. XL-IV. 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 pedicellaria: are found in the genus 



