312 
In the large plurality of species the gonothecae are ringed, 
and with the exception of a single species (S$. tamarisca) the 
hydrothecae are regularly alternate. 
As in most genera the form and direction of the hydrothecae 
are subject to great variation, but in opposition to what is found 
in more or fewer species of all the other genera, the turning of the 
hydrothecae towards the frontal surface of the colony is never so 
strong that the hydrothecae of the two opposite series come in 
contact with each other, and this cannot be regarded as a conse- 
quence of the alternate arrangement of the hydrothecae, as such a 
coalescence is found both in Hydrallmania and in Idia, the hydro- 
thecae of which are alternate. 
In opposition to what is found in all other genera with many 
species the arrangement of the hydrothecae is exceptionally con- 
stant, opposite hydrothecae having hitherto only been found in $. 
tamarisca. 
In respect to the extent in which the hydrothecae are adnate 
to the respective axis Sertularella is the only genus, in which a 
number of species have their hydrothecae only affixed by their 
bases (S. quadrata Nutt., S. catena Allm., S. cylindritheca Allm., 
S. magna Nutt.), and, besides, in a large number of species the 
adcauline wall of the hydrothecae is only adnate in its proximal 
third or fourth (f. inst. in $. areyi Nutt., $. amphoriformis Nutt., 
S. fusiformis Hincks, .S. tricuspidata (Alder) e. t. c.), a condition 
which outside the genus Sertularella has only been found in a few 
species of the subgenus Abietinaria. Only in a few species (& 
lata Bale, S. distans Allm., S. albida Krp.) are the hydrothecae 
adnate in their whole length. 
Corresponding primitive conditions are also presented by some 
species in the structure of the diaphragma, and by others in the 
composition of the colony. 
While all other members of the family seem to possess a com- 
plete diaphragma perforated by a narrow abcauline, pearshaped or 
ovate opening, the diaphragma in a number of Sertularella-speeies 
