104 PLUMATELLA EMARGINATA. 



7. Phtmatella emarginata, AUman. PI. VII, figs. 5 — 10. 



Specific character. — Ccenwcium adherent, creeping ; cells C3'lindrical, witli a very distinct 

 furrow, which gives an emarginate appearance to tlie orifices, and becomes continuous below, 

 with a prominent keel. Tentacula about forty. (Free) Statoblasts elongated. 



Synonyms. — ISOi. Tubulariu repens ? VaTichei-j Bull, de la Soc. Philom., ann. xii, No. 81, 

 pi. 19, figs. 1, 2, 3, 9, 10. 

 1816. Plumatella repens? Lamarck, An. sans Vert., 1st edit., vol. ii, p. 108. 

 1824. A^aisa repens? Deslongchamps, Encyc. Meth., Zooph., p. 561. 

 1836. Plumatella repens? Lamarck, An. sans Vert., 2d edit., vol. ii, p. 123. 

 l&ii. Plumatella emarginata. AUman, Ann. Xat. Hist., vol. xii, p. 330. 

 1847. Plumatella emarginata. Johnston, Brit. Zooph., 2d edit., p. 404. 



Iconography. — Possibly Vaucher's figures of his Tubularia repens ; otherwise no pubhshed 

 figure. 



Habit.^t. — In streams and rivulets, adhering to the under side of stones. 



Localities. — British In a beautiful little rivulet near Bandon, County of Cork. In 

 the River Dodder, near Dublin, abundant. In a rivulet near Arklow, in the County of 

 Wicklow, and in localities furnishing a similar habitat in other parts of Ireland. G. J. A. 



Foreign .- Lago di Como. G. J. A. — France r Vaucher. 



The well-marked furrow in this species, commencing near the orifice in a transparent, 

 triangular space, looking as if a piece had been cut out of the margin of the orifice, suggested 

 the specific name, as this Polyzoon was, at the time of its discovery, the only species known 

 with a similar condition of the ectocyst. Subsequent search, however, has brought to light 

 several others with the same character ; and though the name has thus lost its exclusive 

 appropriateness, it has been nevertheless deemed convenient to retain it. 



This Polyzoon is more opaque and coriaceous than P. repens. The ectocyst, except 

 in the immediate vicinity of the orifices, and at the commencement of the furrow, is loaded 

 with minute, irregularly angular, siliceous particles, giving it under the microscope the 

 appearance of being in a great measure composed of agglutinated sand. It is of a ferruginous 

 colour, becoming lighter towards the orifices, while tlie uniform diameter of the branches 

 deprives it of the peculiar concatenated disposition which is generalh^ so striking in 

 P. repens. It is irregularly branched, adhering closely to the surface on which it grows, 

 but frequently sending off several short free branches of about half an inch in length. 



P. emarginata, unlike most of the other fresh-water Polyzoa, delights in rapid rivulets, 

 though it also flourishes luxuriantly in the more quiet waters of lakes. It is eminently light- 

 shunning ; for though it loves the purest and clearest waters, it is always found on the 

 under surface of stones, where scarcely a ray of even repeatedly reflected light can reach 

 it. It occurs in greatest perfection during the summer and autumn ; at the latter period the 



