FROM THE CORAL RAG. 251 



between the areolas and the poriferous zones there is another band of granulations, 

 composed of three rows of larger granules, among which a few secondary tubercles rise at 

 intervals (fig. 1 e), so that this species has wider granulated inter-tubercular bands than 

 any other Acrosalenia. 



The large apical disc is oblong (fig. 1 a), with the vent excentrical, and placed so far back 

 that it encroaches considerably on the single inter-ambulacrum (fig. I g) ; the two anterior 

 pairs of genital plates are the largest (fig. 1 g), the posterior pair are smaller, and the single 

 plate is extremely elongated ; the body is absent, and the plate is represented by a thickened 

 semi-lunar border with a reflected margin (fig. 1 g) ; this plate extends far down the 

 single segment, and appears as if excavated for the passage of the vent (fig. 1 a) ; the 

 ovarials are shield-shaped, and have the perforation for the ducts near their apex. The 

 ocular plates (fig. 1 g) are small heart-shaped bodies, wedged between the genitals and 

 the apices of the ambulacral areas, the three anterior ones are symmetrical, and the two pos- 

 terior unsymmetrical, and slightly produced backwards ; the eye-holes are lodged in the mar- 

 ginal sinus ; the sur-anal plate is large (fig. 1 /), and composed of several pieces ; namely, one 

 central pentagonal plate, two smaller lateral rhomboidal plates behind the first, another pen- 

 tagonal posterior to these two, and four smaller lateral pieces, making in all eight plates 

 (fig. 1 /) ; these five small plates form the anterior wall of the opening for the vent, which 

 occupies nearly the entire area of the single ovarial plate (fig. 1 g) ; the surface of the 

 discal elements is covered with the same-sized delicate granules (fig. 1/) as those which 

 adorn the miliary zones (fig. 1 d). 



The base is concave, the mouth opening large, one half the diameter of the body ; the 

 sides are tumid and rounded, so that the mouth appears to lie in a deep depression (fig. 

 1 b) ; the peristome is decagonal and nearly equal-lobed, the notches are wide and have 

 the margin reflected all round the rim (fig. 1 h) ; the equatorial tubercles are extremely 

 prominent, and their bosses are conoidal, with deeply crenulated summits (iig. 1 i). 



The primary spines (fig. 1 h) are seen in situ in the specimens on the slab (fig. 1 /:), some 

 of them are one and a half the diameter of the test ; they are sub-cylindrical, subulate, and, 

 to the naked eye, appear smooth, but with the lens are seen to be finely striated ; they 

 are often slightly curved near their bases, and have their milled rings set obliquely ; the 

 head is small and conical, and the milling of the ring not well marked (fig. 1 /) ; a trans- 

 verse section shows that the stem is slightly flattened (fig. 1 /). 



The secondary spines (fig. 1 m) are very small, rather stouter in proportion to their 

 length, and more distinctly striated than the primary spines (fig. 1 m) : the head is larger, 

 and the milled ring more prominent. 



Affinities and differences. — This species differs so much from all its congeners, that it 

 cannot be mistaken for either of them. In its general character it approaches Acrosalenia 

 spinosa, but is distinguished from that species by its pentagonal form, the smallness of 

 the superior inter-ambulacral tubercles, the concavity of the base, the width of the notches, 



33 



