H. L. Hawkins — A Neiv Fibularia from Nigeria. 299 



the petaloid region of the ambulacra, nor any pores like those of the 

 petals in any other part of the areas excepting on the peristomial 

 margin. 



Below the petaloid part of the areas the plates become considerably 

 larger, increasing in both height and width. At the end of the petals 

 the transverse sutures are practically horizontal, but below the 

 ambitus they become oblique to a variable degree, sloping downwards 

 towards the interradial margins of the areas. The height of the plates 

 remains constant throughout the non-petaloid region. On the actual 

 border of the peristome, one pair (rarely two pairs) of pores occur in 

 each ambulacrum. These pores are not quite so large as those of the 

 petals, and only become visible when the specimen is stained. 



On all the plates from the petals to the peristome, there occur, 

 instead of the normal pore-pairs, rows of minute perforations similar 

 to those in Echinocyamus pusillus and many other Clypeastroids. The 

 main series of them form transverse rows, parallel with, and 

 immediately adoral to, the transverse sutures. Towards the inter- 

 radial sutures these rows curve slightly in an adoral direction, and 

 mingle with scattered pores (often grouped obscurely in sets of three) 

 which occur over the whole plate area. The relations of these small 

 pores are shown in PI. XVI, Fig. 9. They can only be seen in stained 

 specimens, and then usually with difficulty. On slightly etching one 

 example with acid, their disposition was clearly shown. The figure 

 is adapted from that specimen, the tuberculation being inserted from 

 a different individual. 



The Interamliilacra. — Between the petals the interambnlacra are 

 very narrow, and, through almost half that region, are composed of 

 single deltoidal plates bearing vertical rows of tubercles. The areas 

 widen out towards the distal end of the petals, but are soon narrowed 

 by the renewed expansion of the ambulacra. The plates are, for the 

 most part, rather higher than broad, and one of them corresponds to 

 rather more than two of the extra - petaloid ambulacrals. The 

 tuberculation is sparse, and uniform in character. The tubercles are 

 deeply scrobiculate, and appear to be imperforate. On the adoral 

 surface the interambnlacra become rapidly narrowed towards the 

 peristome. I have not been able to trace the plate sutures with 

 certainty in this region of the test, but the evidence seems to indicate 

 that there is a single, narrow plate separating the ambulacrals on the 

 peristomial margin, as in the majority of the Clypeastroida. 



The Peristome. — The peristome is central and small, being only 

 0-9 mm. in diameter in specimen B, the largest examined. It is 

 obtusely pentagonal in outline, the angles of the pentagon corre- 

 sponding to the radii. The mouth opening is wider on the outer 

 surface of the test than within, and on the bevelled edge of the 

 peristome one, or more rarely two, pairs of large pores are situated. 

 (In specimen B there seems to be a single pore only in each ambulacrum, 

 proportionately larger than in cases where two pores exist.) 



The Periproct. — The periproct is situated about midway between 

 the peristome and the ambitus (when measured tangentially). It is 

 always smaller than the peristome. The aperture is almost circular 

 in most cases, sometimes showing a slight elongation in the direction 



