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



*Pourtalesia hispida (PI. XXII. figs. 6-19; PL XXXIX. figs. 34, 36; PI. XLI. 

 figs. 47, 48). 



Pourtalesia hispida, A. Agassiz, 1879, Proc. Am. Acad., vol. xiv. p. 204. 



This species mainly difi'ers from its nearest ally, Pourtalesia jeffreyd, AVy. Thomson, 

 in having a shorter anal snout, a more flattened actinal surface, a smaller actinal plastron, 

 and a smaller number of larger primary tubercles arranged in horizontal rows across the 

 primary plates. Its outline is more rectangular anteriorly, and more nearly vertically 

 truncated. 



Seen from above (PI. XXII. fig. 7), the sides of the test are nearly parallel, wdth very 

 slightly re-entering sides, the anterior edge of the test is at right angles with the sides, 

 and the posterior part of the test is conical with a small rounded snout. 



The primary spines are arranged in distant rows of three or four along the sides of 

 the test (PI. XXII. fig. 6); they are quite short, stout, sharp, more crowded along the 

 abactinal keel, and are still more numerous immediately above the anal system (PI. XXII. 

 figs. 7, 9, 12). The anterior slope of the test carries small closely-packed miliaries 

 (PI. XXII. fig. 13), except on the edge and in the deeply-sunken actinal groove where 

 the spines are large and closely packed (PI. XXII. fig. 8), extending across the actinal 

 groove on the actinal side. The primary spines are also more numei'ous on the rounded 

 keel formed by the anterior interambulacral areas (PI. XXII. fig. 8), and most closely 

 packed on the small actinal plastron. The rest of the broad flat actinal surface carries 

 distant irregularly-arranged primary spines. The rest of the test carries but few miliaries 

 or secondaries. Seen in profile the anterior extremity is nearly vertically truncated and 

 rounded anteriorly, the apical system and apex corresponding. The line of the actinal 

 surface is nearly flat, curving upwards to form the lower edge of the anal snout. The 

 abactinal line is also regularly arched, but falls suddenly above the anal opening and is 

 indented where it forms the abactinal line of the anal snout (PI. XXII. fig. 6, 9). This 

 is less developed than in any other species of the genus Pourtalesia. The subanal 

 fasciole is not clearly defined, it extends round the sharp anal snout as a broad band of 

 miliaries with ill-defined edges, both exterior and interior. 



Seen from the anal extremity, the anal system is placed in a deep triangular pit with 

 rounded sides (PI. XXII. fig. 12). 



There are in this species four genital openings (PL XXII. fig. 19), each connected 

 with a well-developed genital pouch (PL XXII. fig. 18). The four genital openings are 

 situated in the trivium (PL XXII. fig. 19), and this is well separated from the bivium by 

 supplementary interambulacral plates. In alcohol the colour of the test is of a greyish- 

 pink, the spines of a lighter tint ; at the base of the .spines the test is of a darker colour 

 forming a deep patch which extends to the miliary ring. Both in this species and in 

 Pourtalesia phiale, the primary spines are comparatively short, sharp, and stout, and are 

 quite regularly arranged over the surface of the test. 



