06 THE VOYAGE OF H.M.S. CHALLENGER. 



shallow grooves, follow the directions of the stem and branches with parallel course, 

 each ridge preserving its integrity for a long distance, except on the pore-bearing face 

 of the flabellum, where the ridges are interrupted by the prominent cyclo-systems. 

 The branches are somewhat swollen at the points where cyclo-systems are attached to 

 them. The whole ccenosteum is, as in other Stylasteridse, permeated by networks of 

 canals. The axes of the branches are traversed by bundles of large main canals, which 

 place the cyclo-systems in relation with one another. 



The cyclo-systems are all, with one exception, which is evidently abnormal in the 

 present specimen, placed on one face of the flabellum, with their axes at right angles 

 to its plane. The systems appear as globose bodies, with flattened tops, which are 

 much wider in diameter than the branches on which they rest, and stand out promi- 

 nent and entirely free from one another, at regular intervals along the course of the 

 branches. The globose appearauce of the systems is due to their being each encircled 

 by a broad prominent zone of confluent ampullae, which zone has a rouuded surface 

 rendered somewhat irregular by the occasional prominence of individual ampullae. 

 Immediately above this zone, the edge of the summit of each system appears as a 

 delicate lamina, which slightly overhangs the outer wall of the system all around 

 (PI. II. fig. 8). The summits of the systems are circular in outline, with a series of 

 indentions in the marginal lamina, as in Allopora 2 )ro f im d a > corresponding with the 

 centres of the outer ends of the pseudosepta. A diagrammatic view of a cyclo-system, 

 as viewed from above the mouths of the pores, is given on Plate II. fig. 15. 



The arrangement of the pores in the systems is closely similar to that in Stylaster 

 densicaulis and Allopora profunda. There is a centrally -placed gastropore in each, 

 which is surrounded by a ring of dactylopores with slit-like mouths. The gastropore 

 in the present genus, however, appears in the form of two chambers, an upper and 

 a lower, which communicate with one another by a constricted aperture. The upper 

 chamber (PL II. fig. 8, GP) communicates with the exterior superiorly by a short 

 tubular passage, bounded by the inner ends of the pseudosepta. The walls of the 

 chamber are curved, so that, taken in conjunction with its upper prolongation, it is 

 flask-shaped. At the base of the chamber its walls are curved inwards, so as to bound 

 a horse-shoe shaped aperture, which leads to the lower gastropore chamber beneath. 

 The aperture is rendered horse-shoe shaped by the projection from its margin on 

 one side of a tongue-like process of calcareous matter, which is directed horizontally, 

 with a slight upward curve across the aperture, reaching as far as its centre (PL II. 

 fig. 8, B ; fig. 15, A). 



The tongue-like process is a solid calcareous structure of a bent conical form, with a 

 rounded extremity. It is grooved on its under surface in the direction of its length, 

 and springs from the margin of the wall of the upper chamber of the gastropore, 

 which is thickened in this region by its stout roots. The process always points in 



