315 
integritheca group by the transformation of the hydrothecal roof 
into an operculum. In either case I cannot doubt but that Ser- 
tularella is a polyphyletic genus. 
Idia Laraouroux. 
(PI. V, figs. 18—22). 
The obliquely ascending aperture is surrounded by two very 
thin lips, which are bordered on each side by a small tooth, and 
are provided with a very mucli convex free margin. While the 
presence of an abcauline opercular membrane is only faintly indi- 
cated on eacli side by the bounding of the lateral tooth, there is 
found a large, well-defined adcauline sinus, which is divided into 
two lateral halves by a well-developed median tooth, and the ad¬ 
cauline opercular membrane, which is provided with a median 
fold and with a free valvular portion, is in opposition to the abcau¬ 
line lip very movable. 
In the only species hitherto known the two series of sub- 
alternate hydrothecae are with the exception of the outwards bent 
distal ends, in the pinnules (but not in the stems) adnate to each 
other along the frontal surface of the colony. The gonothecae 
are urn-shaped, and with the exception of the short broad aperture 
their surface is divided into a number of longitudinal belts. 
In the structure of the hydrothecal margin and the opercular 
apparatus this genus presents the greatest likeness to Hydrallmanici , 
but it differs from this genus in the possession of a median ad¬ 
cauline tooth, and therein that an abcauline opercular membrane 
is only faintly indicated by the abcauline bounding of the lateral 
teeth. 
Also in the possession of subalternate hydrothecae, and in the 
more or less extensive coalescence, which takes place between the 
two opposite series, the species of Hydralhnania show likeness to 
Idia pristis. 
All man 1 ) who has misunderstood both the structure of the 
>) 5. 
