Certain forms of this genus are liable to become compacted together in such a way as to constitute solid masses consisting of elongate vertical zooecia closely parallel to one another and sometimes agglutinated by means of a gummy substance. These forms were given by Lamarck in 1816 the name _Alcyonella_, and there has been much dispute as to whether they represent a distinct genus, distinct species, or merely varieties or phases of more typical forms. It appears to be the case that all species which produce vertical branches are liable to have these branches closely packed together and the individual zooecia of which they are composed more or less greatly elongated. It is in this way that the form known to Allman as _Alcyonella benedeni_ is produced from the typical _Plumatella emarginata_. Other forms go further and secrete a gummy substance that glues the upright zooecia together and forces them to elongate themselves without branching. In these conditions the zooecia become polygonal in cross-section. It is probable that such forms (_e. g._, _Plumatella fungosa_ (Pallas)) should rank as distinct species, for the gummy secretion is present in great profusion even in young zoaria in which the zooecia have not yet assumed a vertical position. No such form, however, has as yet been found in India, and in any case it is impossible to regard _Alcyonella_ as a distinct genus. _Key to the Indian Species of_ Plumatella. I. Ectocyst more or less stiff, capable of transverse wrinkling only near the tips of the zooecia, never contractile or greatly swollen; zooecia rounded[BF] at the tip when the polypide is retracted. Free statoblasts elongate; the free portion of their swim-ring distinctly narrower at the sides than at the ends. A. Ectocyst by no means rigid, of a uniform pale colour; zooecia never emarginate or furrowed, straight, curved or sinuous, elongate, cylindrical _fruticosa_, p. 217. B. Ectocyst rigid; zooecia (or at any rate some of the zooecia) emarginate and furrowed. _b_. Ectocyst darkly pigmented over the greater part of each zooecium, white at the tip; branching of the zoarium practically dichotomous, profuse, as a rule both horizontal and vertical; zooecia straight or slightly curved or sinuous _emarginata_, p. 220. _b'_. Ectocyst colourless and hyaline; branching of the zoarium sparse, lateral, irregular, horizontal; zooecia nearly straight, strongly emarginate and furrowed _javanica_, p. 221. _b''_. The majority of the zooecia distinctly L-shaped, one limb being as a rule adherent; ectocyst never densely pigmented. beta.