153 BRITISH STR0MAT0P0R01DS. 



logist, and wliicb is now in the British Museum. My identification of Stromatopora 

 mammillata, Fr. Schmidt, with D'Orbigny's species, is based upon specimens of the 

 former kindly given me by Magister Schmidt himself. I have figured a portion 

 of the surface, and also tangential and vertical sections of one of these specimens 

 (Plate XIX, figs. 10 — 12). These will show that there exists no substantial differ- 

 ence between the Russian and the British specimens, which I have here included 

 in the present species. Any apparent differences which are present may probably 

 be accounted for by the fact that the Esthonian specimens are silicified, and have 

 therefore undergone considerable alteration. 



Distribution. — Clathrodictyon striatelhim , D' 'Orb., occurs in the Ordovician Rocks 

 of Esthonia (in the " Borkholm'sche Schichton ") ; but elsewhere it is only known 

 as a Silurian species. It is common in the Wenlock Limestone of Britain (Dudley, 

 Ironbridge, Dormington, &c), and it is also found in the Wenlock Limestone of 

 Wisby, Gotland. 



Family— LABECHIQLE. 



Genus 1. — Labechia, Edwards and Haime, 1851. 



(Introduction, p. 81.) 



1. Labechia conferta, Lonsd. sp. PI. Ill, figs. 7 — 15, and PL XX, figs. 1 and 2. 



Monticulabia conferta, Lonsdale. In Murchison, Silurian System, p. 688, 



pi. xvi, fig. 5, 1S39. 

 Labechia — Milne-Edwards and Haime. Polypiers foss. des Terr. 



Pal., p. 280, 1851. 

 _ _ — Brit. Foss. Corals, p. 269, 



pi. kii, figs. 6, 6 c, 1855. 

 — — Nicholson. Ann. and Mag. Nat. Hist., ser. 5, vol. xviii, 



p. 11, 1886. 



Ccenosteum usually in the form of a laminar expansion of variable thickness, 

 attached by a basal peduncle, and having the rest of the lower surface covered 

 by a concentrically wrinkled epitheca (Plate III, figs. 7 and 8). Upper surface 

 without monticules, covered with prominent, rounded or elongated, often conical 

 tubercles, the apices of which may be imperforate, or which exhibit a minute 

 circular summit-aperture. Often the tubercles become coalescent to a greater or 

 less extent, and give rise to vermiculate ridges (Plate III, fig. 13). The surface 

 between the tubercles is smooth, and no astrorhizal grooves are developed. 



