W. G. Van Name — Bermuda Ascidians. 381 



Michaelsenia tincta, n. sp. 



Plate LIV. Figures 61 and 63. Plate LIX. Figure 109. 



The examples found contain only a few zooids, from two or three 

 to a dozen, and do not often measure more than 15 mm across or 3.5 mm 

 in thickness at any point. The surface is finely wrinkled and 

 uneven, often raised over the positions of the zooids, and the edges 

 of the colony are thin and produced some distance beyond the zooids. 

 It is practically free from all incrusting matter. The test-substance 

 is tough and leathery, and opaque, except that about the edges of the 

 colony, or in other places where it is thin and slightly pigmented, it 

 is more or less translucent. The zooids and the test vessels (which 

 have elongated club-shaped bulbs) can usually not be distinguished 

 through it, and in many specimens the number and location of the 

 former can only be seen by the slightly projecting apertures, which 

 do not show their square or four-lobed shape when they are con- 

 tracted, unless the zooid is removed from the test. 



The color is a rather dull carmine-red, deeper about the apertures 

 and paler near the edges and in the lower parts of the colony. 

 Where the pigment is scarce, the test becomes yellowish. When 

 sectioned and stained the test is seen to have a fine fibrillar structure. 



The largest zooids measure from 5 to 6 mm in length and 2 to 2.4 mm 

 across. They lie pn the ventral surface, with the anterior end 

 turned more or less abruptly upward, bringing the branchial orifice a 

 little way back from the end, and are much flattened dorso-ventrally. 

 The atrial orifice, which like the branchial is situated at the summit 

 of a low conical projection, is placed at a varying distance from the 

 posterior end. 



The mantle, especially the dorsal part, is colored a bright carmine 

 by pigment grains contained in its cells. These grains are situated 

 near the periphery of the cells, the central part remaining clear. 

 The mantle-muscles are weak and not gathered into bands. 



There are a great many slender tentacles of two or three sizes, 

 none of them very long. 



The branchial sac has three or four distinct folds on each side. 

 On each fold there are about three internal longitudinal bars, and 

 usually one on each intervening space. The internal longitudinal 

 bars are thus situated at unequal distances apart, there being some 

 six or eight stigmata between them in some jflaces and only about 

 two on the folds. The large transverse vessels number about 

 fifteen, but between each pair there is usually a more slender inter- 

 mediate vessel. The stigmata (which are narrow) often run past 



