116 THE VOYAGE OF H.M.S. CHALLENGER. 



two slight undulations. From its point of attachment it is traceable for a short distance 

 along the ventral edge, imbedded in the test. The upper and the lower ends are both 

 thickened, elsewhere it is of uniform thickness. 



The branchial aperture is large, prominent, and very conspicuous. It is situated at 

 the anterior end and is terminal and median, being directly under the curve of the 

 peduncle (PI. XI. fig. 8). It has the form of a long transverse slit, gaping consider- 

 ably, and bounded by prominent, smooth, dorsal and ventral lips. It looks directly 

 anteriorly. 



The atrial aperture is situated at the posterior extremity of the dorsal edge, just 

 where it passes over into the posterior end. It is sessile, but large and conspicuous, and 

 has the form of a transverse elliptical slit gaping slightly and bordered by smooth anterior 

 and posterior lips. It is directed dorsally and slightly posteriorly. 



The surface is regular, but rough all over from the presence of minute pointed papilke. 

 Surrounding the atrial aperture, and cutting off about a third of the body, is a band of 

 slightly larger papillae forming a ridge like those already described in Culeolus murrayi 

 and Culeolus recumbens. In this species the band is not broad but is compact and 

 continuous, and of the same breadth throughout its course (PL XL fig. 8). It runs 

 from the sharp angle formed by the junction of the ventral edge and the posterior end 

 across the side of the test in a slightly undulating course to cut the dorsal edge at the 

 highest point in its curve, about one-third of the distance from the anterior to the 

 posterior end. It runs therefore from the most posterior point of the body anteriorly and 

 dorsally. The surface of the peduncle is slightly roughened, but it has no sharp papillae. 



The general colour of both body and peduncle is an earthy brown. Closer 

 examination shows that the ground colour of the test is really much lighter, being a pale 

 greyish brown, and that the darker effect is due to the presence of the numerous fine 

 papilla? which are of a very dark brown. 



The dimensions are as follows : — 



Length of the body (antero-posterior), .... 8 mm. 



Breadth of the body (dorso-ventral), .... 5 - 5 ,, 



Thickness of the body (lateral), . . . . . 5 ,, 



Length of the peduncle, ...... 5 cm. 



Thickness of the peduncle, ...... - 5 mm. 



The Test is thin, but tough and rather stiff. It is quite opaque. Its outer 

 surface is very rough from the presence of a great number of minute, closely 

 placed, dome-shaped, or pointed papillae, which are scattered all over it. Each of 

 these papillae stands in a little area of the test separated off by a slight ridge, and the 

 papillae are so closely placed that these ridges divide the entire surface of the test into 

 diamond-shaped, hexagonal, or polygonal areas (PL XIII. fig. 2). These ridges, as well 

 as the papillae, are of a blackish brown colour, while the tint of the remainder of the test 

 is much liohter. There is no foreign matter adherinp; to the surface of the test. 



The surface of the peduncle is slightly uneven, and examination under a low power of 



