264 PERCY SLADEN TRUST EXPEDITION 



20. Donatia ingalli (Bowerbank). 

 (Plate 48, fig. 3.) 



Tethea ingalli Bowerbank [1872 a]. 

 Teihya ingalli (pars) Sollas [1888]. 

 Tethya ingalli (pars) Lindgren [1898]. 

 Teihya lyncurium var. h. Dendy [1905]. 

 Donatia Ingalli (pars) Hentschel [1909, 1912]. 



This is much the commonest form of Donatia in the collection, being represented by 

 seventeen specimens. These range in form from a flattened crust, with wide-spreading 

 base and strongly convex upper surface (R.N. ex. 7), to the usual subspherical form with 

 root-like processes of attachment spreading broadly over the substratum. The surface 

 is usually more or less strongly tessellated in polygonal areas. The colour in spirit is 

 yellowish grey. The subspherical specimens attain a diameter of about 25 mm. 



The cortex is some three or four millimetres in thickness and densely charged 

 throughout with large spherasters forming an almost solid mass. 



The spicule-bundles of the main skeleton penetrate the cortex and spread out into 

 brushes beneath the surface as usual, but there are, usually at any rate, no loose, radially 

 arranged megascleres beneath the cortex and between the bundles. 



The large spherasters (Plate 48, figs. 3 a, 3 h), when fully grown, range from about 

 0'08 to 0"14 mm. in diameter, with rays about half as long as the diameter of the large 

 centrum. Though most abundant in the cortex they are often common also in the 

 choanosome, where they may be associated with numerous much smaller forms*. Some- 

 times comparatively small forms, with very short rays, occur in the cortex just beneath 

 the surface (R.N. cxiii. 1 B, fig. 3 a). In the larger forms the rays may occasionally 

 branch (R.N. cxix. 10 b). 



The cortical chiaster is a typical tylaster (fig. 3 c) with usually more than six rays, 

 from about 0'012 to 0'016 mm. in total diameter. 



The choanosomal chiaster ranges from a typical tylaster (fig. 3 d) to an oxyaster or 

 strongylaster (fig. 3 d') with many short rays, which may be slightly roughened, and 

 a total diameter of about 0'012 to 0"02 mm. 



The chief distinguishing features of these specimens are the great thickness of the 

 cortex, the close-packed arrangement of the spherasters in the cortex, and the sti'ong 

 tendency of the choanosomal chiasters to lose the heads of the rays and assume the form 

 of many-rayed oxyasters. 



I base my conception of this species upon Bowerbank's original description, the 

 emended description by Sollas, and my own study of one of Bowerbank's specimens. 

 1 conclude that the " Sealark " and Ceylon specimens differ from the Australian types in 

 the shorter rays and less strongly developed spination of the choanosomal oxyasters. As 

 regards these spicules the typical form seems to approach D. seychellensis, while differing 



* I have in all the species assumed that these small choanosomal forms are immature and have not 

 included them in the range of size. 



