To this group belongs the eyeless _Hydatina_, a classical object of study, common in greenish pools, whose male was the first male Rotifer to be figured by Ehrenberg (1838), though he did not recognise its nature, and gave it the name of _Enteroploea hydatina_. _Rhinops_ has the back of the corona curiously prolonged forwards into a sort of proboscis bearing two eyes. Some species of _Notommata_ and _Proales_ are distinctly annulated; in _Taphrocampa_ the segmentation is so marked as to give the appearance of mesenteric septa extending inwards from the body-wall to the intestine. _Microcodon_ has a wreath which is very peculiar in its extreme simplicity, with the mouth nearly central, and the eye lying just dorsal to the mouth. The Triarthridae, which resemble the Scirtopoda in having strong leaping spines fringed by fine bristles, should perhaps be placed in the next sub-Order. SUB-ORDER B. LORICATA.—Ploima with a firm elastic cuticle {225}of definite form, persistent after death, continuous, or divided by thinner strips into plates or shields, which again may be areolated. The cuticle may also be shagreened or embossed in various ways. Fam. 15. Rattulidae: _Rattulus_ E., _Mastigocerca_ E., _Coelopus_ G., _Diurella_ (?) Eyfurth. Fam. 16. Dinocharididae: _Dinocharis_ E., _Scaridium_ E., _Stephanops_ E. Fam. 17. Salpinidae: _Salpina_ E., _Diaschiza_ G., _Ploesoma_ Herrick, _Diplax_ G., _Diplois_ G. Fam. 18. Euchlanididae: _Euchlanis_ E., _Dapidia_ G., _Apodoides_ Joseph. Fam. 19. Cathypnidae: _Cathypna_ G., _Distyla_ Eckstein, _Monostyla_ E. Fam. 20. Coluridae: _Colurus_ E., _Metopidia_ E., _Monura_ E., _Mytilia_ G., _Cochleare_ G., _Dispinthera_ G. Fam. 21. Pterodinidae: _Pterodina_ E., _Pompholyx_ G. Fam. 22. Brachionidae: _Brachionus_ E., _Noteus_ E., _Schizocerca_ Daday. Fam. 23. Anuraeidae: _Anuraea_ E., _Notholca_ G., _Eretmia_ G. The group includes a number of very minute forms, besides others conspicuous both for size and beauty. A soft dorsal flap above the head occurs in _Stephanops_; also in Coluridae, a large family of minute species, where the flap is movable, and looks in profile like a hook overhanging the forehead. The genus _Pterodina_, like _Pedalion_ and _Triarthra_, combines a Bdelloid disc with malleoramate trophi, while its exsertile wrinkled foot ends in a ciliated cup like that of a larval tubicolous species. _Brachionus_, a large, often flat, transparent form, with a long wrinkled foot, is a very common genus, known to the earlier observers, and repeatedly figured by them. _Pompholyx_ has a sack-like lorica, no foot, and carries its immense egg suspended by an elastic thread from the cloaca. The Anuraeidae lack the foot, and often have great spines or bristles projecting from the lorica, which no doubt facilitate floating. They are abundant in the "plankton" or floating fauna of large lakes far from the shore. Many marine species belong to this family.