15G W. H. HARRIS ON MARINE MICROSCOPIC VEGETABLE ORGANISMS. 



Probably the majority of forms known as Lacunce are merely a phase or 

 condition in the life history of the plants, or possibly the initial stage of a 

 filamentous species. Plate 9, Fig. 2 x 210. 



Lacuna radiata. — The flask-like cavity of this species is rather deeply 

 immersed in the containing fragment : the neck-like portion is considerably 

 elongated and very small in diameter. 



The exterior surface of the globular portion is distinctly mammillated, and 

 from each apex, liranched or unbranched, very fine hair-like processes are 

 produced, which reach the surface. 



They usually occur separately, but I have seen indications of two becoming 

 confluent ; spore-like bodies having an amber tint are present in some 

 instances ; these escape through an eroded aperture, which destroys the 

 neck-like portion of the organism. 



Widely distributed, but not very common. British material has furnished 

 the best examples — notably Kenfig Pool, Bristol Channel. 



Found in shallow- water deposits. Plate 9, Fig. 3 x 210. 



Lacuna radicans. — This species is very variable in form, and may consist 

 of a simple or unbranched central cavity, or they may assume various con- 

 tours according to the number of branches they produce. 



The central cavity, however, is tolerably large, and gives ofE at fi*equent 

 intervals, around the margin, very fine and freely branched filaments, usually 

 decreasing in size towards their extremities. 



Alwaj's solitar3\ 



Not common. Occurs in material from Morte Bay, and in another 

 gathering, the precise locality of which I have been unable to ascertain. 

 Plate 9, Fig. \ x 1.50. 



Jjacuna incerta. — This organism appears to be allied to L. ftjyorangifcra , 

 but there arc distinf^tivo features which render its identification compara- 

 tively easy. 



It alwaj'S occupies a superficial position in the shell ; the central cavity is 

 large, exceedingly irregular in form, and the surface is thickly perforated, 

 giving it a sieve-like appearance. 



In some specimens numerous processes are given off from the margins ; 

 these are slightly expanded towards the base, and terminate in hair-like 

 filaments, or the expanded portion may be absent, the fine filaments alone 

 being present. 



They multiply by forming young plants near the ends of the fine filaments 

 when these reach the surface. 



Rare. In material from Java Sea and Macassar Straits, 45 fathoms. 



Lacuna moniliformis. — This organism consists of a series of irregular- 

 shaped JjacwKc connected by filaments, which, when fully developed, are 

 freely branched and liberally provided with short excretory ducts. 



This is one of a few plants met with which appear to occupy an inter- 

 mediate position between the genera Lacunce and AclilycB ; the character- 

 istic features of both are so intimately combined and balanced that valid 

 objections could be raised against a preference being created for either as 



