SPONGES, ZOOPHYTES, AND SEA-FIRS. 63 



Fam. Lafoeidse. 



Genus Lafoea. In L. dumosa height may reach four inches, stems 

 erect and irregularly branched, or simple and creeping, cups 

 tubular and numerous, arising from all sides of the stem. 



Fam. Halecidce. 



Genus Halecium. In H. halecinum ("herring-bone" coral) height 

 may reach ten inches. Stems rigid, much branched. Cups 

 sessile in two rows on projecting processes, alternate, tubular. 

 Gonothecfe on upper surface of stems, broad and truncate 

 above, with tubular orifice at side. 



Fam. Sertularidoe. 



Genus Sertularella. In S. polyzonias the cups are urn-shaped, 

 bulging below, with a divergent four-toothed aperture. Gono- 

 tliecre shortly stalked and large. Stems slender, much but 

 irregularly branched. 



Genus Sertularia. In S. pumila the sterns are loosely branched, 

 the gonothecse have a tubular rim. 



Genus Hydrallmania. In H. falcata ("sickle -coralline") the 

 stems are about a foot long, slender, and with spirally- 

 arranged branches. Gonothecae yellow and tubular. 



Genus Thuiaria. In Thuiaria thuia ("bottle-brush") the stem, 

 which may be one foot in length, bears a cluster of branches 

 at the top. Cups in two rows. 



Fam. PlumularidtB. 



Genus Plumularia. In P. setacea the slender, delicate stems are 

 about one inch in height, the plumes arise separately from 

 the creeping stolon. Joints of branches alternately long and 

 short, zooid-cups placed singly on the long joints. For 

 nematophores, see figure. Gonothecoe with long tubular 

 necks. 



NOTE ON DISTRIBUTION. 



The Sponges and Sea-firs described in this chapter are so common 

 that they may be expected at almost any part of the British area, 

 where the conditions are at all favourable. Their relative abundance 

 at different places varies considerably, however. Thus Hydractinia 

 echinata, which is extraordinarily abundant at St. Andrews and in 

 the Firth of Forth, is much less common in the South and West. 

 Again, at places like Torquay and Penzance, not only may many 

 other species be expected on the shore in addition to those mentioned, 

 but a happy chance may furnish the "Portuguese man-of-war" 

 (Physalia), to which reference has been made above, and other beau- 

 tiful free-swimming forms, swept in by ocean currents from the open 

 sea. Though generally vspeaking the South and West are richer in 

 Hydrozoa than the North and East, yet there are one or two forms 

 which occur in the latter and not in the former localities. The 

 interesting "bottle-brush" (Thuiaria thuia}, for example, is said to 

 be rare off the coasts of Cornwall and Devon. 



