176 PROF. F. JEFFREY BELL ON THE [Mar. 1, 



on tlie north-west coast of Australia, are a number of young 

 Echiuoderms ; in many cases it is not possible to assign them a 

 definite specific place, but to the morphologist they will offer charms 

 less patent to the systematist. 



Among them there is an Ophiurid which is remarkable for the 

 large size of what are now generally regarded as the plates of the 

 calycinal area, and which my lamented friend P, Herbert Carpenter 

 in his valuable essay ^ called respectively centro-dorsal, under-basals, 

 and radials. These plates are so well marked that it is quite im- 

 possible for the most sceptical to regard them as anything else than 

 the components of a vestigial calyx, and I think their relations to 

 the rest of the organism are perhaps better shown in the drawing 

 given herewith than in any previously published figure of an Ophiurid 

 (Plate XL figs. 6, 7). 



It is certain that the specimen is the young of a species of Pectinura 

 or of some form closely allied to that genus. 



2. Classification of Ophiuroids. 



Since the year 1867, when Dr. Ljungman^ published his still 

 valuable classification, no serious attempt has been made to classify 

 the Ophiuroidea, and it is possible that some doubts remain as to the 

 relations of the genera that compose that class ; the question whether 

 the simple-armed Ophioderma or the much-branched Astrophyton 

 has the more archaic characters is one which systematists have 

 neither asked nor answered. The majority of naturalists would 

 probably confess that their impression was that the many-branched 

 forms had succeeded those with simple arms. 



At any rate all are agreed that there are two equivalent orders or 

 groups — the Ophiurse and the Euryalse of Johannes Mtlller, the 

 Ophiuridae and Astrophytidse of Theodore Lyman ; if these two 

 groups are really sharply separated from one another, it will follow 

 that we must look upon one as derived from the other and now 

 separated from it by the disappearance of the connecting-links, or 

 we must suppose that they had long ago a common ancestor and 

 have since been evolved along distinct *lines ; the latter is the view 

 adopted by Prof. Haeckel in his ' Generelle Morphologic.' 



Mr. Lyman, though retaining the bifid division of the class, 

 recognizes the resemblance of some of the Ophiuridse to the Astro- 

 phytidse, for his "group in." is called " Astrophyton-like Ophi- 

 urans." One striking point in which Sigsbeia and Hemieuryale, for 

 example, two members of the group, resemble Astrophyton is the 

 power of rolling their arms. KwA. the function has a corresponding 

 similarity of structure. Li most brittle-stars the " several ossicles 

 of the arm have a certain power of movement on one another, but 

 this is limited by the development of processes and pits analogous 

 to the zygosphenes and zygantra of the Ophidian vertebrae. In such 



1 Quart. Joum. Micr. Sci. xxiv. (1884) pp. 1-23. 

 ■^ Ofv. Vet.-Atad. Forhandl. xxiii. (1867) p. 303. 



