REPORT ON THE TUNICATA. 305 



the present specimen, the tubercle is of large size (1*5 mm. 

 in diameter). The outline is perfectly circular, and the 

 horns have evidently united on the right side so as to form a 

 ring-shaped structure with no aperture. 



Polycarpa monensis, n. sp. (PI. V, figs. 1-8). 



External Appearance. — The shape of the body is trans- 

 versely ovate, the dorso-ventral diameter being the larger. 

 There is slight lateral compression and the body is not 

 attached. The surface is rough and irregular from the 

 presence of attached stones and other foreign objects. The 

 colour, where the test is visible, is a dull grey. The length 

 of the body (antero-posteriorly) is 1*5 cm. ; the breadth 

 (dorso-ventrally) is fully 2 cm. ; the thickness (laterally) is 

 1*2 cm. 



The Test is thin but firm. It has shell fragments, and 

 small stones attached firmly to its outer surface. There are 

 no adhering processes. The test matrix is clear and trans- 

 parent. There are no bladder-cells, and the test-cells are 

 small and inconspicuous. 



The Mantle is thin and has the musculature feeble. It 

 is closely adherent to the inner surface of the test through- 

 out. The sphincters are moderately strong. Over the rest 

 of the mantle the muscle fibres run in all directions, and 

 form a close but delicate network. 



The Branchial Sac is not very large. Its walls are 

 delicate. There are three or four folds upon each side. 

 Each fold has about five closely placed internal longitudinal 

 bars upon its surface, while there are one or two bars only in 

 each interspace. The transverse vessels are narrow, and all 

 of much the same size. The meshes are square or slightly 

 elongated transversely. Each contains from four to six rather 

 wide stigmata, and is divided transversely by a narrow 

 horizontal membrane. On the right side of the endostyle 

 there are four rows of meshes of which the most ventral is 



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