446 DB. G. J. HINDB ON NEW FOSSILS [Aug. 1 896, 



fibres precisely similar to that in recent corals. Though in reality 

 compact, under certain conditions of preservation, microscopic sec- 

 tions of it give the erroneous impression of being traversed by 

 minute tubuli. 



It will be seen on comparing these two forms, Palceacis cunei- 

 formis, M.-Edw., and Hydnopora (?) cydostoma, Phill., that the 

 differences between them are of too radical a character to allow of 

 their inclusion in the same genus. In the former the walls are 

 simply perforated by mural pores or canals analogous to those in 

 Palaeozoic Favosite corals, while in the latter there is a distinct 

 lacunar ccenenchyma, similar to that in modern perforate corals, 

 and moreover the interior of the calices has a solid non-perforate 

 layer which carries the blunt septal spines or tubercles. Minor 

 differences are the wrinkled outer surface and the attached mode 

 of growth in H. (?) cydostoma. 



Of the other species referred to Palceacis, that herein described 

 as P. humilis approaches nearest the type- species. 1 P. obtusa, 

 Meek & "Worthen, sp. ( = P. cymba 2 and P. umbonata, 3 Yon 

 Seebach), P. compressa, 4 M. & W., sp., and P. enormis, M. & W., sp., 

 form a group markedly distinct from the type-species of the genus 

 and P. humilis in the larger size of the corallum, the openly conical 

 and shallow form of the calices and the much greater thickness of 

 their walls. As regards the structure of the walls in these forms 

 nothing definite is as yet known. In the specimens of P. obtusa 

 from Spergen Hill, Indiana, belonging to the British Museum 

 (Natural History), which I have examined, the interior is now a 

 solid mass of silica and all traces of pores or canals have been 

 obliterated, and it therefore remains an open question whether they 

 were similar to P. cuneiformis in this feature or not. The principal 

 grounds for including them under Palceacis, M.-Edw., are their 

 general form, striated or ridged outer surface, and free condition 

 of growth. 



[Since this paper was read Mr. E. T. Newton, F.R.S., has brought to 

 my notice a specimen of Palceacis obtusa, Meek & Worthen, sp., from 

 the Carboniferous Limestone of Hook Point, Wexford, Ireland, now 

 in the Jermyu Street Museum, in which the structure has not been 

 altered by silicification, so that the character of the wall in this 

 species can be determined. The specimen in question (PI. XXIII. 

 fig. 18) is partially weathered out on the surface of a piece of lime- 

 stone ; it is wedge-shaped, free, about 13 mm. in width, and nearly 

 the same in height. There are six shallow, openly conical corallites 

 at the summit. The outer surface is covered with fine, somewhat 

 wavy striae or ridges, which have a general direction towards the 

 centre of the base ; in places they are discontinuous and interrupted. 

 A vertical median section shows that the corallite-walls are regu- 

 larly perforated by pores and canals, which connect adjoining 

 calices and also pass through to the exterior (PI. XXIII. fig. 18 a). 



1 Geol. Surv. Illinois, vol. ii. (1866) p. 233, pi. xvii. figs. 2 a-e. 



2 Zeitschr. deutsch. geol. G-esellsch. vol. xviii. (1866) p. 309, pi. iv. figs. 4 a & b. 

 3 _Ibid. figs. Sa & b. * Op. jam cit. p. 234, pi. xvii. figs. 1 a-c. 



