188 Proceedings of the Royal Thy deal Soeiety. 



whilst the perforations, unlike those of Synapta and Cheirodota, 

 do not appear to be toothed or serrated. 



The plates in Holothuria papillosus are flat and fiddle- 

 shaped. In other species they are circular, with a stellate 

 center, or with a spine projecting from the middle (H. intesti- 

 Qialis, Ascanius) . The integument of H. (?) floridana (Pourtales) 

 is filled with spicules in the form of an irregular cross or star, 

 whilst other Holothuria? possess bundles of calcareous bodies 

 like a slightly curved rib, with a small perforated expansion 

 at each end. In H. trcmula the plates are small and oblong, 

 with a series of perforations arranged in lines, giving to the 

 organisms much the appearance of a portcullis door. 



The genus Cucumaria possesses spicules of varied form. 

 In C. frondosa (Linn.) they are plume- like, with slightly 

 serrated edges. C. Hyndmanni (Forbes) has strange looking 

 bodies like a bent dumb bell, with a perforated enlargement 

 at each end and in the centre. Similar spicules exist in 

 C. canescens (Semper), but they are rather more curved. 



Some plates in the British Museum, labelled Cucumaria, 

 possess wheel-like plates resembling those of Cheirodota ; the 

 perforations, however, are less regular, and the central space is 

 subdivided. 



The anchors and anchor-plates of Sijnapta are replaced in 

 the genus Cheirodota by peculiar wheel-spicula scattered 

 throughout the integument. They are composed of a central 

 axle-hole, from which radiate spokes, uniting with the outer 

 margin or tire. The apertures or spaces thus enclosed are 

 triangular, and have the inner margins of the tire notched or 

 scalloped. In C. violacca the spaces are five or six in number ; 

 in C la^vis there are very regularly six. 



The dermal plates of Myriotrochus Rinhii (Steenstrup), an 

 arctic form, are more complex, although on the same plan. 

 The radiating subdivisions are from eighteen to twenty- 

 three in number, with other intermediate shorter projections, 

 and very elongated and narrow enclosed spaces. 



Lastly in Ka-plodactyla molpadioides (Semper) are four- 

 radiate spicula resembling those of some sponges. 



The foregoing is only an outline of some of the more 

 interesting forms of plate-structure amongst recent Holothur- 



