DE. W. A. HEEDMAN ON BEITISH TUNIC ATA. 277 



on neither dorsal nor ventral edge, while the intestine, though 

 still curving away from the heart, turns posteriorly instead of 

 anteriorly. 



"We thus see that it is possible, by a simple change in the re. 

 lation of the alimentary canal to the branchial sac, to get the very 

 different arrangements of the viscera found in the genera Corella 

 and Ascidia from the simpler and somewhat intermediate condi* 

 tion which obtains in Ciona. This explanation also accounts for 

 the curious position of the heart in Corella, and shows that it is 

 merely a consequence of the change in the disposition of the 

 intestine. 



Some of our British species of Ascidia require examination ; 

 several have been described under different names by different 

 authors, and many have never been sufficiently characterized — a 

 full description requiring, according to our modern ideas, an 

 account of the condition of the branchial sac, dorsal lamina, and 

 other internal organs, as well as of the external appearance. 



The new species have been dredged, during the last three 

 summers, on the west coast of Scotland, in Loch Long (Clyde), and 

 in Lamlash Bay, Arran. 



Ascidia lata, n. sp. (Plate XIV. figs. 1-3.) 



External appearance. — Shape roughly oblong, anterior end nar- 

 rowest; flattened laterally ; nearly erect; posterior end rounded; 

 ventral edge convex ; dorsal edge with a large rounded projection 

 near the middle. Attached by a small oblong area at the ventral 

 edge of the posterior end of the left side. Branchial aperture 

 terminal or nearly so, sessile, not conspicuous ; atrial aperture 

 about halfway down, placed at the summit of the projection on 

 the dorsal edge, not conspicuous, lobes rather indistinct. Surface 

 smooth, but cut up by faint creases, most of which, are longitu- 

 dinal and on the upper (right) side ; a few Serpulce &c. adhering 

 towards the posterior end. Colour yellowish grey, light at 

 anterior end, and brownish, towards posterior end and on lower 

 (left) side. Length 9*2 centims., breadth 5*1 centims. 



Test rather thin, thickish on the upper surface, and especially 

 at the area of attachment. Yessels well-developed and conspi- 

 cuous on the inner surface ; trunks enter near the middle of the 

 ventral edge. 



Mantle moderately developed ; musculature strong on the 



