that I propose to include in the sections Patèlla-Balanus and Armato-Balanus^ and at the same 

 time of the known species of Acasfa, might lead to a somewhat different conclusion — but 

 with our present knowledge I think the best we can do is to bear in mind the near relation- 

 ship existing between the two genera, and at the same time to avoid bringing together too 

 closely what after all, perhaps, should be kept apart. 



i. Acasfa conica n. sp. PI. XXIY, hg. 11 — 16. 



Carino-lateral parietes narrow, hardly one tenth of width of lateral parietes; inner sur- 

 face of parietes distinctly ribbed, outer surface smooth in the lower half and looking as if 

 covered with scales in the upper half. Scutum broadly triangular, the outer surface delicately 

 striated longitudinally, the articular ridge feebly developed ; tergum with a deep longitudinal 

 furrow and the spur obliquely-truncated, not quite one fourth of width of valve. Basis conical, 

 its edge feebly crenated. Upper segment of pedicel of 4 th cirrus with a row of well-developed 

 teeth, lower segments of anterior ramus of same cirrus with groups of such teeth near the 

 extremity of their inner faces. 



This species (PI. XXIV, fig. 11) belongs, no doubt, to the same group of species as 

 A. spongites Poli and A. sulcata Lamarck. All the specimens I have seen were very small. 

 Their colour is greyish-white, the occludent margin of the scuta having a black colour. The 

 orifice is rather large and distinctly toothed, the tips of the compartments being pointed, and the 

 summits of the alae and radii very oblique. These tips are somewhat curved inwards — but 

 not so strongly as is the case in A. nitida. The surface of the parietes is smooth in the lower 

 half, covered in the upper half with rounded scale-like patches, the exact nature of which I 

 have not been able to discover. I can only say that the rounded patches on being examined 

 with the microscope turn out to represent thinner parts of the wall. Small calcareous projections 

 are clisposed here and there on the surface; they seem to occur more generally and in greater 

 numbers on the rostrum and carina than on the lateral valves. The inner surface of the valves 

 is distinctly ribbed ; these ribs do not quite reach to the basal margin of the valve. The edge 

 of the basis is delicately crenated, but the little teeth of that edge do not correspond to 

 the ribs of the valves, the latter bein^ much less numerous. The radii extend down to the 

 basis, but their summits are very oblique and their free edge is in contact with the adjoining 

 latus over less than half the length of that latus. The surface of the radii shows feeble hori- 

 zontal lines crossed by still less distinct oblique striae. The alae are about the same width 

 as the radii, but they do not extend down to the basis. The basis is not very deep but 

 distinctly conical. 



The size of one of the larger specimens is: total height 4.5 mm., of the capitulum 

 without the basis over 3 mm. Greatest basal diameter 3.5 mm. 



Scutum (PI. XXIV, fig. 12, a and c) triangular with the basal margin strongly convex, 

 the basi-tergal angle much rounded off. Growth ridges very prominent, distinct till close near 

 the apex. Outer surface moreover, distinctly striated longitudinally, the striae extending from 

 the apex down to the basal margin. The upper part of the occludent margin is coloured 



