CLASS II HOLOTHURIOIDEA 313 



those made known by Giebel from the Lithographie limestone of Solenhofen. 

 These he called Protholoturia, and though the material does not permit of exact 

 generic determination, it bears a resemblance to certain Recent species of 

 Holothuria and Pseudosiichopus. The impression formed by the general appear- 

 ance of these specimens that they really represent Holothurians is confirmed 

 by the presence of characteristic calcareous particles on their surface. 



Recently, in the remarkably well - preserved fauna from the Middle 

 Cambrian shales of British Columbia, Walcott has discovered some complete 

 specimens of typical Holothurians, preserving many details of the original 

 animals. Most of these species are referred by A. H. Clark to the family Elpi- 

 diidae (a group of very remarkable Holothurians at the present time confined to 

 the deep sea),"but one of them, Eldonia (Fig. 435 bis), representing the new family 

 Eldoniidae, was free-swimming like the Recent Pelagothuria, though structurally 

 entirely difFerent from that type, being most nearly related to the Elpidiidae. 



Dissociated calcareous particles referred to Holothurians have been 

 described by a number of writers from the British Carboniferous rocks, the 

 Zechsbein of Germany, the Lias and Dogger of Lorraine, the Upper Jura of 

 Franconia, the Cretaceous of Bohemia, the Eocene of Paris, the Oligocene of 

 Offenbach, the Pliocene of Italy and the post-Tertiary of Scotland. A very 

 large majority of these cannot be assigned to any particular genus or even 

 family of Holothurians, and it is probable that many if not most are of other 

 than Holothurian origin. There can be no question, however, that a part 

 of this material is of real paleontological value. In particular the forms 

 described by Schlumberger and by Spandel are worthy of attention. 



Spandel's discovery of what seem to be unquestionable Holothurian 

 spicules, like those characteristic of the genus Chiridota, in the Zechstein of 

 Germany, is noteworthy. These spicules are distinctly wheel-shaped, but 

 differ noticeably from those of Recent Chiridota in having 10-14 spokes instead 

 of six. They thus show a certain resemblance to the wheels of Trochoderma 

 and the first formed calcareous deposits of the larvae of Chiridota rotifera and 

 certain Auricularias. Spandel's later discovery of an Oligocene Synapta, and 

 Schlumberger's studies on the Eocene Holothurian spicules of the Calcaire 

 Grossier, show that during the Tertiary period the Synaptidae were already 

 difFerentiated into the three Recent subfamilies, Synaptinae, Chiridotinae and 

 Myriotrochinae. Beyond this grouping we cannot speak with any certainty. 



Our actual knowledge of fossil Holothurians may be summed up as follows : 



1. Holothurians allied to living members of the class existed in the Jurassic 

 seas of Europe, and, according to Walcott's Interpretation, there is evidence 

 that the typical expression of the group was already differentiated as early 

 as the Cambrian. 



2. Holothurians of the family Synaptidae, allied to Chiridota or Trochoderma 

 occurred in the Permian seas of Europe ; and at least as early as the Eocene, 

 all three of the Recent subfamilies of Synaptidae were differentiated. 



3. The Permian Holothurian spicules are wheel-shaped but have numerous 



spokes as in Trochoderma, and resemble those of the larval Chiridota, not those 



of the adult. 



[The account here given of Holothurians, with the exception of the paragraph in regard 

 to Cambrian repräsentatives of the class, has been contributed by Dr. H. L. Clark of the 

 Harvard Museum of Comparative Zoology.— Editor.] 



