114 



such plates, placed close together on a more strongly calcified and proximally 

 sharply defined part of the zocecium. The same is the case in Brettia frigida, 

 and I shall only mention further, that whilst the zooecia in the uniserial branches 

 are as regards rosette-plates provided in quite the same way as the zooecia in 

 the many-rowed branches, they lack the holes on the other hand in the proximal 

 portion of the lateral wall, which in the zooecia with several rows, correspond with 

 the rosette-plates on the neighbouring zooecia. 



Petalostegus nov. gen. 

 Catenaria p. p. 

 The membranous frontal area is covered by a circle of mutually connected 

 plate-like or leaf-like hollow spines; a slightly chitinous, semicircular, simple 

 operculum; sessile aviculana; free (?) ooecia; zooecia in one row. 



P. bicornis Busk. 



Catenaria bicornis Busk, Challenger, Zoology, Vol. X, PI. 1, pag. 14, PI. 2, 



figs. 2 a, 2 b. 



— — Waters, Challenger, Zoology, Vol. XXXI 1, p. 9, PI. 1. fig. 1. 



(PI. IX, figs. 8 a, 8 b). 



The zooecia widened upwards from a long, narrow, tube-shaped proximal 

 part, oblique quadrangularly oval, strongly arched especially on the frontal sur- 

 face, the largest part of which is formed by a membranous area, covered by five 

 mutually coalesced hollow spines. These, which spring from the rim of the frontal 

 area with a relatively narrow proximal part, have a broad rhombic form and 

 are therefore in the marginal part of the frontal area separated bj' four wide, 

 but low interspaces, which are bounded externally by the edge of the frontal 

 area, internally by the proximal edges of the rhombic spines. At the two distal 

 spines the corresponding space is formed by the aperture itself. The distal much 

 longer portions of the spines are each furnished with 2 — 3 very short projections, 

 which meet with corresponding projections from the adjacent spines, and the 

 five radial sutures are thus provided with 2 — 3 larger or smaller oval pores. 

 Of the five spines the proximal is the largest, and meets with the two distal in 

 a triradiate suture, whilst the two others which are the smallest do not reach 

 in to the middle of the area. The rhombic form of the three larger spines thus 

 becomes somewhat modified, in such a way that the proximal spine is strictly 

 irregularly hexagonal, and the two upper pentagonal. The aperture, which is 

 placed a little proximally to the distal edge of the zooecium, is almost semi- 



