E. M. Brydone—New Chalk Polyzoa. 295 



at the head of the zooecium with a depression between it and the 

 aperture ; in the q%iadratus form they are exceptional, being large and 

 globular. 



Avicularia small, mandibular, very abundant, and typically placed 

 interstitially at every meeting-point of four zooecia, with the beak 

 directed upwards, and generally, but not (e.g. Fig. 3) invariably, in 

 the zones of M. cor-testudinarium and M. cor-anguinum fused with the 

 surrounding zooecia. In the zone of H. planus they are wide (about 

 •3 mm. at maximum width) and stumpy with circular apertures, from 

 the lower side of which a slender sinus runs a short way downwards 

 in the middle line. In the zone of M, cor-festudinarium they are 

 reduced in width by about half, the side walls rise considerably, the 

 beak when distinguishable is long and narrow, and the aperture is 

 smaller in proportion, definitely elliptical, and often without sinus, 

 the latter when present being much reduced in length. In the zone 

 of M. cor-anguinum the lateral compression has increased to a point 

 at which they are often little more than wide cracks between the 

 zooecia; the aperture when visible is still elliptical, but narrower, and 

 shows no trace of a sinus. In the zone of A. quadratus the avicularia 

 are apparently much shorter and wider again, but one of the side 

 walls seems to have been squeezed upwards and inwards until it 

 almost wholly overhangs and conceals the aperture ; the outlines of 

 the avicularia are very faint and uncertain. 



The early and late forms of this species differ so markedly from the 

 general type that they might easily be treated as separate species, 

 and it is only the progressive series afforded by the avicularia which 

 has decided me to act on a strong general impression that they are all 

 variations of one very plastic species. I propose, however, for the 

 present to distinguish the planus form as var. lateaperta and the 

 quadratus form as var. peneclausa. 



The form described by D'Orbigny as Reptescharinella transversa 

 comes near this, but is easily distinguishable by the avicularia pointing 

 downwards. 



Semieschara Woodsi, mihi.^ (PL XV, Figs. 1-5.) 



Semieschaea Peegensi, mihi.^ (PI. XV, Figs. 6-11.) 



I take this opportunity of giving photographic figures of these 

 species, as the original figures, which were based upon my probably 

 diagrammatic sketches, are not very adequate. In each case the type 

 is unfortunately not well adapted to photography, and has required 

 to be supplemented by other specimens. In the case of S. Woodsi 

 I am now convinced that what I described as the upper lip of the 

 aperture sloping sharply inwards is the upper surface of the butt end 

 of the succeeding zooecium, visible within the upper part of a large 

 semicircular aperture ; round pores are sometimes visible in its end 

 wall, and this is well shown by several zooecia of the type-specimen, 

 which was therefore specially lighted to bring out this feature as far 

 as possible. The aperture of the avicularium seems very variable 

 both in size and shape, the prevailing shape being elliptical, not 



1 Geol. Mag., July, 1906. 



