On the Scattered Skeletal Remains of Holotliuroidea. 187 



attached to the smaller end of each plate, by means of an 

 articulating process, of more or less complex form, and either 

 on the convex or concave side (S. Galliennii). This process 

 is at times simple, or it may possess a slit like the eye of a 

 needle {S. digitata, Montg,), or it is in the form of a raised 

 arch {S. vittata, Forsk.), or, again, the plate is devoid of any 

 process at all {S. inhcerens, Miiller). 



The anchors themselves vary much in minute structure. 

 They are plain and simple (iS'. vittata) ; long or short ; and 

 stout and straight {S. hidentata, W. and B.). The flukes are 

 plain, or barbed on the convex margin (aS'. inhcerens), or both 

 in the same species. The apices^of the flukes are occasionally 

 reflexed (S. Galliennii), and at other times bifid (S. hiden- 

 tata, W. and B.). In one species the anterior or convex 

 border is marked by a central depression (S. Thomsoni, 

 Herapath). The shaft is terminated by a plain crosspiece, 

 with recurved ends, or it may be serrated, and sometimes 

 deeply divided. Lastly, in S. Goddefroyi (Semper), the proxi- 

 mal termination of the shaft in the anchors is triradiate. 

 Generally speaking, the discrepancy in size between the 

 plates and anchors is considerable, the latter being the larger. 



The skin of the Synaptm also contain additional particles 

 termed by Woodward and Barrett " miliary granules." They 

 vary considerably in size. 



In the genera Thy one {T. fusiis, Miiller) and Thyonidium 

 (T. pelluciduni, Vahl) the calcareous plates are of a more 

 irregular form than in Synapta, and have usually a much 

 greater number of perforations. The latter are also plain and 

 non-serrate, and are by no means as large in proportion to the 

 size of the plates they pierce. Some of the plates in T. fusu& 

 are provided with an elevated and arched process, which sub- 

 divides into two outstanding limbs, each bifid at the free 

 extremity. There is likewise a well-developed, lesopliageal 

 ring, or spurious lantern, composed of long, elongated, tooth- 

 like pieces. The spicula in the tentacles of Thyone raphanus 

 are of a remarkably dendritic or aborescent form. 



Most fantastic forms are assumed by the calcareous plates 

 in some species of Holothuria, Cucitmaria, Mulkria, and 

 Stichopus. They are dendritic, star-like, irregular, or C-shaped, 



