178 SALENIA 



ambulacra narrow, two complete rows of marginal granules, and a few small central ; inter- 

 ambulacra wide, two rows of primary tubercles large in the upper part, small below ; 

 apical disc half the diameter of the test, plates roughened with raised points ; each ovarial 

 plate with five furrows leading to the large sutural pores. Spines slender, cylindrical, 

 finely striated and granulated, the longest exceeding If inches in length, and less than one 

 line in diameter ; frequently forked at their extremities, and sometimes bent and otherwise 

 distorted. 



Dimensions. — Height, nine twentieths of an inch ; latitude, thirteen twentieths of an 

 inch. 



Description. — This very distinct form of Salenia has an elevated body, depressed and 

 flattened on the upper and under surfaces ; the ambulacral areas are narrow and straight 

 (fig. 1 d,) with two complete rows of marginal granules, about twenty in each ; within these 

 are two incomplete rows of small irregular granules, having a microscopic granulation 

 scattered around their base. Fig. 1 g shows an ambulacral area magnified four times, 

 and exhibits the increase in volume of the marginal granules near the base of the area. The 

 poriferous zones are narrow ; the pores form oblique pairs with a thick septum between, and 

 having a small granular elevation on the surface : fig. 1 h shows this structure magnified 

 six diameters, as well as the minute granulation on the surface of the plates, and the 

 comparative sizes of the marginal and central granules in the area. The number of pores 

 opposite each large plate is eight or nine pairs. 



The inter-ambulacral areas are wide above and narrow below ; there are six primary 

 tubercles in each of the two rows, and of these the four above the ambitus are much the 

 largest ; those on the under side are much smaller and set closely together ; all the tubercles 

 have wide areolar spaces, which are encircled for three parts of their circumference with a 

 series of large, remote, well-developed granules. Fig. \f shows an entire inter-ambulacral 

 space magnified four diameters, and fig. 1 h a single plate with its primary tubercle, 

 areolar space, and circle of marginal granules, with the poriferous zones and ambulacra, 

 magnified six diameters. The miliary zone (fig. 1/) is wider below the ambitus, and is 

 here filled with an abundant granulation (fig. 1 c, fig. 1/) ; above the ambitus, the large 

 size of the tubercles diminishes the width of the zone, and the tubercles here are fewer 

 and larger (fig. 1/, fig. 1 b, and fig. 1 d). 



The apical disc is one half the diameter of the test, and the surface of the plates is 

 roughened with many raised points (fig. 1 b) ; each ovarial plate has five furrows leading 

 to the sutural pores, which have an arrangement similar to the punctuations on the disc 

 in S.petalifera ; a semicircle of seven punctures indicates the sutures by which the sur-anal 

 is united to the three anterior ovarials ; one large and two smaller punctures mark the 

 line of union between the ocular and ovarial plates. In fig. 1 e the apical disc is magnified 

 four diameters ; and the sutural punctuations are very correctly delineated in this drawing. 



The spines of Salenia Clarkii are very well preserved with the test in the unique 

 specimen belonging to the Museum of the Royal School of Mines, and which I have figured 



