114 



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

 sharply defined part of the zoa^ciuni. The same is the case in Brettia fri(jida, 

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

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

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

 portion of the lateral wall, which in the zoa?cia 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 mulually connected 

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

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



P. bicornis Busk. 



Catenaria bicornis Husk, Challenger, Zoologj', Vol. X, PI. 1, pag. 14, PI. 2, 



figs. 2 a, 2 b. 



— — Waters, Challenger, Zoology, Vol. XXXI^, 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 by 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 wilh corresponding projections from the adjacent spines, and the 

 five radial sutures are thus j)rovided 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 triradiale suture, whilst the two others which are the smallest do not reach 

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

 becomes somewhat modified, in such a way that the proximal s])iiie is strictly 

 irregularly hexagonal, and the two u])per pentagonal. The aperture, which is 

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



