7()0 Proceedings of the Royal Irish Academy. 



the bottom, but to be merely seated on, or with their bases slightly 

 embedded in, the stiff mud.^ In the beginning, probably, the founder 

 of the colony starts sedentary life on a more solid object, such as a 

 small stone or shell. A few dead shells are scattered over this ground ; 

 and such extraneous objects as peats, accidentally dropped from boats 

 ferrying turf over from the mainland, form'a suitable nidus for various 

 animals. But since the bulk of the organisms to be obtained by 

 dredging are more or less dependent on the masses of Ascidians for 

 attachment or shelter, these latter certainly are the dominating f eatiu'e 

 of the ground, to which we consequently gave the name Ascidian 

 ground. It is needless to name here the animals taken on this and on 

 the ground to be next considered. Most of the species occurring in 

 the harbour are to be found on these two grounds, as may be seen on 

 reference to the various tables accompanying this report. 



Shell-ieds. — In the channel between Knightstown and Eeenard, 

 and off Gruppaun Point, there are considerable accumulations of shells 

 of Cardium, Mya, and, in particular, Pecten maxinms, with a few living 

 specimens of the last named. Ascidiella aspersa is here absent, or at 

 any rate scarce ; the functions performed by its colonies in the economy 

 of the bottom fauna being taken on by the shells. The results of our 

 earlier explorations pointed to a much more marked difference between 

 the Shell-beds and the adjacent Ascidian ground, with respect to their 

 fauna, than proved on further investigation to be the case. In point of 

 fact, there are a comparatively small number of species peculiar to 

 either ground, though the Shell-beds present a somewhat richer fauna, 

 both in species and individuals. 



There remain in the neighboui'hood of Knightstown several grounds 

 to be noticed : — 



Lough Kay and Caliir Passage. — A strong tide runs through here, 

 and often a considerable swell sweeps round from Doulus Bay. The 

 bottom is rather clean gravel, with a limited fauna, consisting of 

 species also found on the Shell-beds. 



Glanleam Bay. — Clean sand, with very poor fauna apparently; 

 probably burrowing animals exist there which the ordinary dredge 

 fails to capture. 



Mouth of Rarhotir. — The bottom of the channel at the north entrance 

 of the harbour, as far in as the Perch reef, is much- washed gravel and 

 sand. In this, at fii'st sight, barren material live a few characteristic 



1 Ascidiella aspersa may be seen growing in similar fashion on the muddy shores 

 of Salcombe Harbour and the E. Yealm (in Devon), exposed during spring tides. 



