246 



Pterocella n. g. 



The sternal area has 3—7 fenestrse disposed in a curve and a rounded crypto- 

 cyst lamina on its inner surface. The aperture, the posterior part of which is 

 trapeziform or arch-shaped, is provided with two strongly developed, freely pro- 

 jecting hinge-teeth. The lateral chambers form a wing-like marginal portion on 

 either side in the whole length of the zooecium. The mother-zooecium has a small 

 avicalarium on its adzocEcial side. The occlusion lakes place in a way similar 

 to that in Scuticella. 



Pterocella alata Wyv. Thompson. 

 Catenicella alata Wyv. Thompson, Nat. Hist. Review, 1858. 



Pi-oceed. Dublin Univ. Zool. and Botan. Associat. I, pag. 80, 

 PI. VI, fig. 4. 

 (PL XII, figs. 6 a, 6 b, pi. XXI, fig. 4 a). 



The zooecia oval with a number of very small scattered pores and a very 

 strongly arched basal surface with undulating, longitudinal striEe. The sternal 

 area, which is of about the same size as the aperture, is provided with 4 — 6 

 round or oval fenestrae, through which the margin of the inner calcareous lamina 

 can be clearly seen. The plainly visible frontal sinus is occupied by 1 — 3 proxi- 

 mal, rudimentary or very slightly developed spines and further by the two large, 

 distal ones which meet in a sutural line. The two latter sometimes show a small 

 inner cavity. The anter of the aperture is semi-elliptical, and its poster has a 

 straight median portion and two lateral pai'ts obliquely ascending towards the 

 hinge-teeth. 



The lateral chambers form on either.side a distally directed, rounded, tri- 

 angular expansion, the top or the point of which lies at the end of the supra- 

 scapular chamber. The distance between the ends of the two scapular chambers 

 is in a unizooecial internode about the length of the internode, and the two 

 lateral expansions form a distal angle of 120" — 140° with each other. The 

 scapular chamber, which is everywhere developed as an avicularium with an 

 extremely small mandible, has the form of a long, compressed tube, and con- 

 trary to the case in all the above-described species an avicularium appears also 

 on the adzocecial side of the mother-zooecium, where it is situated opposite the 

 distal part of the aperture. It is here however considerably shorter and stands 

 out almost vertically from the surface of the zooecium. The wing-like expansions 

 formed by the lateral chambers are widest in the supra-scapular chamber, from 

 which they decrease iu breadth proximally. The supra-scapular chamber, which 



