452 PROF. W. A. HEEDMAlSr ON KlUTISH TUKICATA. 



antero-posterior length (from the branchial aperture to the area 

 of attachment) being very slight indeed compared with the extent 

 in other directions. Around the edge of the area of attach- 

 ment tliere is a thin margin or expansion, which is in some cases 

 narrow and in others very wide (see figs. 3 & 5). The surface 

 may be rough and corrugated or quite even ; and I could not see 

 that this difference was the result of the state of contraction of 

 the animal, as I had about fifty specimens alive for a couple of 

 days in my tanks at the Port Erin Biological Station, and the 

 corrugated ones did not seem to fill out, although the branchial 

 and atrial apertures were open. Even the characteristic polygonal 

 scale-like markings on the surface of the test are much more 

 distinct in some individuals than in others, and may be emphasized 

 by touches of rose-red upon each scale so as to form a series of 

 lines of spots (see fig, 7). 



The colour of the living animal is generally of a reddish-purple 

 tint, but it may be rose-red or grey with rosy marks, or it may 

 be light yellow to yellowish brown, or finally of a dark purple. 

 The specimens are, on the average, about 1*5 cm. in length. 



The test is tough, although not thick except at the margins of 

 the base. It is white on section and glistening on the inner 

 surface, in places tinged with violet-red, which is specially marked 

 at the branchial and atrial apertures. 



The mantle is fairly muscular, and has a serrated projecting 

 fold or partial diaphragm at the base of the atrial siphon, just 

 in the position occupied by the atrial tentacles in Polycarpa 

 glomerata and other forms. 



The branchial sac has four well-marked folds on each side. 

 The internal longitudinal bars are narrow and ribbon-like. 

 There may be as many as 11 between two adjacent folds, or as 

 few as 4, more usually there are 7 to 9. The meshes are square 

 and contain about 4 large regular stigmata each (PL XXXVI. 

 %-8). 



The dorsal tubercle is nearly circular in outline. The horns 

 are simply turned towards one another and are not bent 

 (PI. XXXVI. fig. 9). 



The dorsal lauguets are very long and slender (PI. XXXVI. 

 fig. 9), and are more numerous than the transverse vessels ; there 

 are from 40 to 60 of them. 



The tentacles are compound and of two very different sizes ; 

 there are about twenty of each. The stems of the lai'ger ones are 

 much inflated (see PI. XXXVI. fig. 9). 



