34 W. PERCY SLADEN. 



the homologies of plates instead of larvae at very early stages, 

 it is hardly to be imagined that any one would have thought 

 of suggesting that the terminal plate should be taken as the 

 homologue of the Crinoid first radial. 



In sequence to the foregoing remarks, it may be stated that 

 the number of Starfishes which maintain these primitive plates 

 (as they may be called) throughout life, and in which the 

 homologies of the crinoidal plates can be studied without 

 having recourse to the larval stages, is much greater than has 

 perhaps been hitherto supposed. It is unnecessary for the 

 present paper to enter into a detailed recapitulation of the 

 different forms by name, and it will be sufficient to say that 

 numerous species comprised in the genera Pentagonaster, 

 Tosia, Astrogonium, Stellaster, Nectria, Ferdina, 

 Pentaceros, Gymnasteria, and even some in Scytaster 

 and Ophidiaster may be referred to. 



Mr. Carpenter's work on the Ophiurids in a former page, 

 with a similar result, has already been spoken of. The points 

 which he has brought to light are of the most interesting 

 description. 



An important feature presented by the larger larvae and the 

 fully-grown examples of Zoroaster fulgens consists in the 

 presence of well-developed under-basal plates (fig. 16, a, 2), 

 which form a circle round the dorsocentral plate internal to 

 the circle of basal plates and radially disposed. These plates 

 are homologous with the under-basals of dicyclic Crinoids 

 (e.g. Cyathocrinus, Encrinus, and Marsupites), and 

 are marked 2, 2 in Carpenter's nomenclature. The presence of 

 under-basal plates is apparently not a rare occurrence in 

 Asteroids; and it may here be remarked that the repre- 

 sentatives of these plates are developed in larval Asterina 

 gibbosa, at a stage later than that studied by Ludwig ' (see 

 fig. 14; 2, and that similar plates which I likewise homologate 

 with under-basals are to be found in young tests of Asterias 

 rubens and A. glac'ialis. They are large and well developed 

 in the adult forms in Pentagonaster' semilunatus, Gym- 

 ' 'Zeitschr. f. wissensch. Zool.,' Bd. xxxvii,- (' Morphol. Studien,' Bd. ii). 



