from the Devonian of Cornwall, 167 



merely of this curious elongation of the arm-segments in general, 

 but of the interspaces between them in this genus (lettered q). 

 An objection to the hypothesis was the necessity for assuming the 

 suppression of alternate podia. Here, it may be, is eyidence of 

 a stage in which those podia were not yet suppressed, though perhaps 

 somewhat atrophied. If both depressions {f and q) were for the 

 reception of podia, then their alternate approximation to and removal 

 from the perradius may be compared with the similar phenomenon 

 in Asterids. 



Whether the features just discussed be or be not accepted as evidence 

 in favour of the compound origin of the Ophiurid vertebra, they 

 demand some explanation; and it may be added that the same 

 hypothesis will perhaps furnish an equally needed explanation for 

 the hitherto unexplained differences that obtain between Palaeozoic 

 genera of Ophiurids in the relations of the adambulacrals to the 

 ambulacrals. 



The origin of the Ophiurid mouth-skeleton also may be illuminated 

 by the preceding hypothesis, which is in full harmony with the 

 opinion that many more arm-segments enter into the composition 

 of that structure than is the case in Asterids, an opinion based on 

 embryological research by Dr. 0. zur Strassen,^ and on palseontological 

 investigation by Dr. 0. Jaekel in the paper quoted above. In this 

 region of the ray, at any rate, adambulacrals and podia must have 

 been suppressed in all Ophiurids. We may here note the apparent 

 absence from our specimen of the adambulacral elements known 

 as side mouth-shields, as well as of the peristomial plates. The latter 

 are wanting in most early Ophiurids, a fact confirmatory of Dr. zur 

 Strassen's conclusion that they are not ambulacral elements, but 

 " secondary calcifications confined to the interradial region." 



Systematic Position. 



In considering the systematic position of this fossil we have two 

 systems to choose from : one, that proposed by Dr. Gregory in 

 the paper above quoted, and adopted by him in " A Treatise on 

 Zoology " (ed. Lankester, London, 1900) ; the other, the latest 

 classification by Mr. B. Stiirtz (Verb. nat. Ver. preuss. Eheinlande, 

 Ivi, p. 198, 1900). The two classifications have much in common, 

 and, without discussing their respective merits, it will be convenient 

 to start with Dr. Gregory's as more accessible to English readers. 



The union of the ambulacrals into vertebrge removes the fossil 

 from the Order Lysophiurse and from the Streptophiuran Family 

 Ophiurinidffi, while the absence of a covering integument or scutes 

 prevents it being placed in any of the other Orders or in any Family 

 of Streptophiurse other than Lapworthuridae or Eoluididaj. Of these 

 two Families the former has no ventral arm-plates, and the latter, 

 while having ventral ones, has no dorsal arm-plates, except in 

 Aganaster. If the exposed surface of this fossil be rightly regarded 

 as ventral, the specimen must belong to the former Family. The 

 genera herein contained are Lapworthura, Greg., Furcaster, Stiirtz, 

 1 Zool. Anzeiger, xxiv, p. 609 ; Nov. 1901. 



