594 W. H. HFDLESTON ON WEST-AUSTBALIAN 



5. Evactinopoka dendeoidea, sp. n. Plate XXIII. figs. 3 a, 3 b, 

 3c, 3d 



In this species the development is dendroid rather than crnciform, 

 the rays or branches being cylindrical to ovate, and even flattened ; 

 whilst the arrangement is possibly triradiate, if we are to regard 

 the specimen fig. 3 a as an original centre or nucleus. The other 

 specimen figured (figs. 3b, 3c, 3 c?) is believed to be a branch from a 

 similar nucleus, and is in a very good state of preservation. All the 

 external peculiarities with respect to the pores and the blank spaces 

 are common to this and the previous species, and a very large series 

 might possibly show connecting links. Still this form would seem 

 to be triradiate rather than quadriradiate, the rays usually, though 

 not always, having a tendency to be cylindrical. 



A weathered fracture in the second specimen (fig. 3 b) gives a 

 good axial section, which has been enlarged (fig. 3 c), but not enough, 

 perhaps, to show the very complex tubular structure, though the 

 lamination mentioned with reference to the previous species is very 

 conspicuous. Indeed the lamination is so brusque that it very much 

 interferes with a correct understanding of the relations between the 

 very fine axial tubes and the larger lateral ones. A study of this 

 specimen seems to indicate that the laminated portion of the general 

 structure is confined to the region of the large lateral tubes, as the 

 central portion is free from lamination and in a somewhat different 

 mineral condition. Owing to unequal development, this ray is 

 very unsymmetrical in this portion of its course, and thus where 

 there is a fresh manifestation of the fine vertical tubing, the absence 

 of lamination again coincides. Whether this has any structural sig- 

 nificance it is impossible to say. 



The transverse section (fig. 3 d) of this same branch, or ray, shows 

 us the tubular systems from a different point of view ; whilst the 

 laminar structure is much less apparent. Here we obtain a good view 

 of the division along the middle by the " thin lamina separating the 

 inner ends of the pores of the opposite sides," the central axis, as it 

 were, of the ray or branch. The relation of the axial or vertical 

 tubes to the lateral ones is never to be made out in these transverse 

 sections; but we learn that the larger tubes are sparingly tabulate*, 

 and we also perceive unequally developed zones of the small tubes 

 at intervals in the more external portions, which are, I suppose, 

 connected in some way with the growth of the stock. 



There are two other specimens in the collection which may belong 

 heref. 



* Dr. G-. J. Hinde has drawn my attention to the circumstance that in 

 Nicholson's work on the Monticuliporidge forms are depicted which, as 

 regards their internal structure, are not unlike Evactincpora. At page 88, 

 Heterodictya, an undoubted polyzoan, is shown to have well-deAeloped tabulas. 



t In the Mem. Soc. Geol. France, 2 ser. t. 2, pt. 1, there is a paper by M. 

 D'Archiac on fossils from the Nummuline beds of the neighbourhood of Bayonne, 

 in which he describes, under the name of Guettardia Thiolati (p. 197, pi. v. fig. 

 15, and pi. viii. figs. 5, 6, 7), an organism somewhat resemblirg this. He re- 

 fers it to Michelin's genus Guettardia, which is generally regarded as a sponge. 



