W. H. HARRIS ON MARINE MICROSCOPIC VEfJETABLE ORGANISMS. 159 



The cavities which terminate the shorter branches are irregular in form ; 

 some are nearly globular, others C3'lindrical, and occasionally they assume 

 the form of little groups of filaments built up like a string of beads, like the 

 reproductive bodies of Penicillum glaucum ; but whatever their form, they 

 occasionally appear to be thickly beset with short hair-like appendages. 



The two species are apparently closely related. I can recommend the 

 study of this organism to intending workers, as the subject is by no means 

 exhausted. 



It has not been observed in any material from outside the British area. 

 Comparatively common in littoral deposits of the Cornish and Devonshire 

 coasts. Plate 9, Fig. 8 x 180. 



Achlya artictdata. — A very well defined species, but rather difficult to 

 detect owing to the plants being rather small and usually rather deeply 

 immersed in the substance of the shell they invade. 



The filaments are composed of numerous elongated pear- or club-shaped 

 joints, articulated in a regular system, the bulbous parts being the growing 

 ends. 



The joints more deeply situate appear to be destitute of appendages, but 

 as they approach the surface rather long simple tubular processes are 

 developed. 



The plants branch rather freely and in moderately thick shells ; several 

 whorls may be observed, causing the organism to assume the form of a bush 

 in miniature. 



Very rare. Found in material from Challenger stations 172 and 187, and 

 in littoral material from Whitesand Bay, Cornwall. Plate 9, Fig. 9 x 300. 



Achlya simjilex. — This is a very well defined and easily recognised species. 

 PkObust in habit. 



Mr. Waller has given an excellent illustration of the peculiar manner of 

 the development of the filaments in Plate XV., fig. 9, which accompanies 

 his paper, but the si^ecimen from which the drawing was made was evidently 

 immature, as in its perfect condition it appears to be a freely branching 

 species. 



The filaments consist of a series of segments of a circle connected in 

 regular succession ; they arise from the convex side, at a point about one-fifth 

 the length of the segment, the free end of which reaches the surface of the 

 shell and perforates it, causing a succession of circular apertures corre- 

 sponding to the size of the filaments. 



Widely distributed, but not common. Appears to be associated with 

 moderate depths. 



Achlya porosa. — This is a very minute species, evidently closely allied to 

 the preceding. 



The filaments are produced in a precisely similar manner, but the branches 

 are generally less regular in their arrangement, and include a wider range 

 of angles than is observed in A. sinqtlex. 



Widely distributed ; not common. Associated with A. simplex in some 

 gatherings. Not observed at a greater depth than 45 fathoms. 



