D. BRYCE ON A NEW CLASSIFICATION OF THE BDELLOID ROTIFERA. 69 



the lumen tube-like, but the outer membrane is not conspicuously 

 of much greater capacity. 



To Section A belong the three new genera, Habrotrocha, 

 Oeratotrocha, and Scepanotrocha. In the first-named the 

 corona conforms with relatively minor modifications to the type 

 usual in the family. In Ceratotrocha that portion of the skin 

 whch supports the upper lip and the lateral cushions of the 

 mouth is produced into two horn-like processes upon whose 

 lower or ventral surface are inset the ciliated discs, the pedicels 

 which usually support the latter being either rudimentary or 

 absent. In Scepanotrocha the upper lip itself is modified into 

 a membranous hood-like expansion larger than the corona, which 

 it completely covers (save the extremities of the cilia), and which 

 it dorsally screens. 



These three genera claim about one-fourth of the species of the 

 Philodinidae. In my opinion they are representative of an 

 earlier stage in the development of the typical Philodine, the 

 genera of Section B representing, broadly speaking, a distinct 

 advance in development, shown hy their greater average size, the 

 greater jwoportional development of the corona, especially of the 

 trochcd discs, and their greater activity, mobility, and boldness. 



The genera of Section B, comprising all Philodinidae in which 

 the lumen is tube-like, divide naturally into three Subsections : 



I. With four toes (two dorsal, two terminal). 

 II. With three toes (one dorsal, two terminal). 

 III. With toes bearing a number of cup-like suckers, or united 

 to form a broad disc, or twin discs. 



Stdisection I., with four toes (the dorsal pair usually somewhat 

 distant from the terminal), In this subsection the remarkable 

 foot of the Bdelloid rotifer attains its highest development. The 

 comparatively wide separation of the two pairs of toes, the 

 independent action of each pair, their consequent control by 

 different muscles and nerves, the rapidity and certainty of their 

 affixment, indicate greater specialisation than is exhibited by any 

 other groups, however closely approached by individual forms. 

 In the same way, the four-toed species surpass their relatives 

 in the development of the corona. The average width of the 

 trochal discs, in some species extremely ample, and its proportion 

 to the body-length are much in excess of those seen in other 



