186 Proceedings of the Boycd Physical Society. 



sight a resemblance to the maxillae of tlie Echini. But as 

 they cannot be used for mastication, — being scarcely movable 

 upon each other, and nowhere reaching the central cavity of 

 the mouth — this appellation is improper."* 



The form of the calcareous plates in the Holothuroidea is 

 very varied; in some genera they are quite simple, but in 

 others more complex. It has been shown by the late Messrs 

 S. P. Woodward and Lucas Barrett -f* that in Synapta the 

 pattern of the anchors and anchor-plates is characteristic of 

 the species to which they belong. In this statement they are 

 supported by Dr W. B. Herapath. J It is clear, therefore, the 

 study of these plates is of the greatest importance to the 

 palseontologist, for by means of them only can he gain any 

 knowledge of pre-existing forms. 



In Bynctj)ta the calcareous plates are usually more or less 

 elongately oval, pointed-ovate, leaf-shaped, obovate, or obcor- 

 date in outline ; the external margin being either plain or 

 serrated [8. Gcdliennii, Herapath). The attenuated end of the 

 plate is produced in a few species into a handle -like process 

 (aS'. duhia, Semper, S. Buskii, MTntosh, etc.). The perforations 

 vary much in number in one plate; usually they are few, but 

 in some species {S. pseudodigitata, Semper, S. similis, Semper) 

 they are very numerous, and much crowded. The margins of 

 the perforations may be plain and entire {S. digitata, Montg.), 

 or they may be scalloped {S. inhcerens, MUller), or the central 

 hole only may be in this condition (S. vittata, Forsk.). In 

 other forms the perforating holes, instead of having the 

 margins serrate, are subdivided by projecting processes {S. 

 Astrolabi, Held, and S. Beseli, Held). As a rule the perfora- 

 tions are on the same plane, or nearly so when the surface 

 is a little convex, but in one species at least they are arranged 

 in a pyramidal form (S. TJwmsoni, Herapath). Those placed 

 at the attenuated end of the plate are smaller and more 

 crowded than on any other portion, although in certain forms 

 the marginal perforations are the smaller {S. digitata, Montg., 

 /S'. Galliennii, Herapath). The " anchors " of Synapta are 



* Pourtales, Proc. American Assoc. Adv. Science (1851), p. 9. 



t Annals Nat. Hist. (1859), iii., p. 214. 



t Quart, Jour. Micro. Science (1865), v., p. 3. 



