from the Devonian of Cornwall. 169 



its receipt in a rather informal letter, extracts from which have 

 since been published by him (Trans. K. Geol. Soc. Cornwall, xii, 

 p. 752, Sept. 1904). One sentence ran: "So far as I can judge 

 without more prolonged study [the fossil] is either Ophiiirina or 

 a close ally." The structure had not then been developed by etching 

 and brushing. It is now quite clear that the specimen has nothing 

 to do with Ophiurina, which is in the Lysophiuran stage, with long 

 rod-like uufused ambulacrals. Mr. Fox has since kindly presented 

 the specimen to the British Museum, where it is registered E 5,036. 

 Horizon. — The rock is certainly Devonian, but on its precise age 

 the present specimen, being of a new generic type, can throw 

 little light. The stage of evolution at which Sympterura stands, 

 namely, primitive Streptophiuran, is fully consistent with a Lower 

 Devonian age. 



Note. — In this paper I have used the term ' ambulacrals ' for the 

 elements of which the Ophiurid vertebra is composed, and in so 

 doing have followed the general custom. But many writers, from 

 Johannes Miiller onwards, have contended that the so-called 

 ambulacrals of Asterids and Ophiurids are not homologous with 

 those plates in Echinoidea for which the term was originally 

 proposed. This contention has much in its favour. At any rate, the 

 so-called ambulacrals of Asterids are homologous with the flooring 

 plates of the subvective groove in Edrioasteroidea, and not with the 

 covering plates, which latter are usually called ambulacrals, as in 

 Pelmatozoa generally. 



For practical purposes also, I have used the ordinal names 

 Streptophiurffi and Lysophiuree, proposed by Mr. F. J. Bell and 

 Dr. J. W. Gregory respectively. But it seems to me that the 

 divisions adopted by my friends and colleagues represent stages 

 of development rather than divergent groupings, and while admitting 

 the great interest and value of the conceptions, I cannot follow 

 Dr. Gregory in ranking them as Orders. 



EXPLANATION OF PLATE VI. 



Fig. 1. — Sympterura, semi-diagrammatic reconstruction of the Sth arm-segment 

 and part of the 7th. a, distal portion of the vertebra ; b, proximal portion ; 

 c, adambulacral ; p, podial depression or pore ; q, interspace, occupied, at 

 least in part, 'by intervertebral muscles, x 18 diam. 



,, 2. — Sympterura, semi- diagrammatic reconstruction of the 2nd arm-segment 

 and part of the 1st. a, b, c,p, q, as in Fig. 1 ; d, border of disc, x 18 diam. 



,, 3. — Sympterura, semi-diagrammatic reconstruction of part of the mouth- 

 skeleton. X 10 diam. 



,, 4. — Lapworthura, diagram of the arm-structure, after Gregory, Proc. Zool. 

 Soc. London, 1896, p. 1037. a, c, p, as in Figs. 1 and 2. 



,, 0. — Bundenbachia, diagram of the arm-structure, after Gregory, op. cit., 

 p. 1034. a, c, b, as in Figs. 1 and 2. Dr. Gregory is not responsible for the 

 lettering in Figs. 4 and 5. 



,, 6. — Sytnpterura Minveri, the unique specimen. The numbering of the rays is 

 for convenience only. In drawing this figure I was helped by preliminary 

 sketches made by Mr. W. Lewis before the specimen was fully cleaned. 

 X 7 diam. 



All figures represent views of the ventral surface. The drawings are reproduced 

 l)y the London Stereoscopic Company, Limited. 



