6 Prof. H. A. Nicholson on some neio or 



Ohs. This species is closely allied to C. vesiculosiwi, Nich. 

 & Mur., and C. variolare, E,os. It differs from both in the 

 want of crumpling- of the concentric laminee and in the 

 resulting fact that the interlaminar vesicles are quadrangular 

 rather than lenticular. It differs further from C. vesiculosum 

 in the greater remoteness of the laminfB, and from C. vario- 

 lare in the approximately uniform width of the interlaminar 

 spaces. Dr. George J. Hinde has been good enough to 

 submit to me a number of examples of this form from Gotland, 

 where it seems to be common ; but I have not found it else- 

 where. 



Formation and Locality/. Wenlock Limestone, Wisby, 

 Gotland {coll. Dr. George J. Hinde). 



Clailirodictyon striatellum^ D'Orb., sp. 

 (PI. I. figs. 9 and 10.) 



Stromalopora concentriea, Lonsdale, Silurian System, p. 680, pi. xv. 



fig. 31 (1839). 

 Stromatopora striatella, d'Ortigny, Prodrome de Paleontologie, t. i. 



p. 51 (1850). 

 Stroviatopora mammillata, Fr, Schmidt, Sil. Form, yon Ehstland, 



p. 232(1858). 

 Stroviatopora mammiUata, von Rosen, Ueber die Natm' der Stromato- 



poren, p. 71, pi. viii. figs. 1-5 (1867). 

 Stromatopora mammiUata, Ferd. Eoenier, Letlisea Palasozoica, part i. 



p. 531, fig. 125 (1883). 



Ccenosteum mostly laminar or hemispherical, with a con- 

 centrically-wrinkled basal epitheca. Surface more or less 

 undulated, but without definite eminences or '^ mamelons," 

 the concentric ]amina3 usually exfoliating concentrically round 

 elevated points. In well-preserved examples the surface 

 shows innumerable small rounded tubercles, representing 

 the crumpling of the concentric laminae, and between these 

 are minute pores. Astrorhizas are apparently wanting. 



As regards internal structure, vertical sections (PI. I. fig. 9) 

 show that the concentric laminae are comparatively remote, 

 about four interlaminar spaces, and therefore five laminae, 

 occupying the space of 1 millim. ; but the interlaminar spaces 

 are wider over the convexities of the undulated laminas. The 

 laminge are thrown into successive undulations, which are more 

 pronounced in some specimens than in others, but are always 

 gentle and regularly curved. The laminse are also regularly 

 crumpled, in the same manner as in C. vesicidosum^ but 

 less completely, so that there is no appearance in vertical 

 sections of rows of lenticular vesicles, such as are so charac- 

 teristic of the latter species. Each infolding of the lamina is, 



