ON A NKW C-.KNUS AND SPFX'IES OF lU.AS TOIDS. 8l 



bulacra, most of them have at the lower end, at the junction with the 

 cokmm, a little projection in form of a cone, which is almost as prom- 

 inent in small specimens as in larger ones. This cone constitutes 

 the lower ]iart of what appears to be a tripartite plate, in form of a 

 clover-leaf, occupying the central portion of the basal disc, into which 

 it extends for some distance, following its curvature. It is frequently 

 somewhat elevated above the general surface of the basals, and can be 

 observed in most specimens with the naked eye. The sutures which 

 separate the basals by their shorter sides, in the usual way, divide the 

 lower leaves lengthwise. From external appearance, one feels very 

 much inclined to take the inner part of the basals to be an independ- 

 ent series of plates; but on grinding the surface there is no intermediate 

 suture. In one of my si)ecimens, which I take to be an extremely 

 large specimen of Peuireinites Godoni, I find within the clover-leaf an- 

 other leaf-like structure, but of less width, and beneath it eight joints 

 of the column, divided longitudinally in the same direction as the 

 basals. The inner leaf is at its border as distinctly marked as the 

 outer one; it extends not far beyond the column, but is considerably 

 wider, and very much higher than the stem joints, which are so ex- 

 tremely short that there are eight joints to a length of half a hne. The 

 structure is such that there can be but little doubt that the inner leaf, 

 although differing considerably in its dimensions from the succeeding 

 stem-joints, is actually nothing else but the proximal joint, which had 

 become enlarged and gradually anchylosed with the basals. It is tpiite 

 evident that the outer clover-leaf had a similar origin. At the outer 

 leaf the sides of the anchylosed joint were more extended, and became 

 almost entirely absorbed into the basal ])lates, leaving only external 

 marks, while at the inner ones tlie column structure can yet be recog- 

 nized, although the joint has here actually become a part of the basal 

 plates. This is the only specimen in which I have observed a second 

 series of plate-like marks, and I do not know whether this instance 

 represents an abnormal case, or is owing to the extreme size of the 

 specimen; at any rate, it gives an explanation how similar marks were 

 produced. 



In corroboration of these views, I will further direct attention to 

 Pentremites abbreviatus Hambach, a very depressed species, in which 

 the basals, even in young specimens, have an almost horizontal posi- 

 tion, and in which, as might be expected, there is no conical projection 

 at the end of the basals. In this specimen, the leaf-like marks are 

 very large and conspicuous; they form a somewhat triangular, clover- 



[Proc. D. a. N. S., Vol. IV.] 11 [Sept. 34, 1884.] 



