GENUS LABECIIIA. 83 



in Ldbeehia no radial pillars, no interlaminar spaces, and, of necessity, none 

 of the vesicular tissue which I have described as filling all the spaces between the 

 radial pillars. 



It is, however, quite beyond question that the skeleton of the English examples 

 of Ldbeehia conferta consists essentially of radial pillars and intervening vesicular 

 tissue, as above described. Some specimens of the same species which Dr. Lind- 

 strom was good enough to send me from the Wenlock Limestone of Gotland, 

 exhibited this structure quite as clearly as our British examples, and I was, there- 

 fore, at first much puzzled with the discrepancy between the phenomena observed 

 in these and the descriptions given by Lindstrom and Roemer. Professor Roemer 

 was, however, so kind as to send me a specimen and slide of the form which had 

 served as the basis of his description of the structure of Ldbeehia conferta, Lonsd. , 

 and which, as coming from Gotland, may be supposed to agree with those that had 

 been under observation by Dr. Lindstrom ; and an examination of this explained 

 the discrepancy in question. The specimen, namely, apparently belonged to 

 Ldbeehia conferta, Lonsd., and, indeed, exhibited a very well-preserved surface ; 

 but the internal structure had been almost wholly destroyed by a process of 

 secondary crystallisation — a phenomenon which is not uncommonly observable in 

 other Stromatoporoids. Hence the radial pillars and intervening lenticular 

 vesicles, which are quite well preserved in certain of the Gotland specimens, had been 

 wholly obliterated, and the observable structure was simply that of a series of 

 undulated and closely superimposed layers, as described by Dr. Lindstrom and by 

 Professor Roemer. Recently, moreover, I have collected a number of examples of 

 Ldbeehia from the Upper Oesel Group (Ludlow formation) of Esthonia, which are 

 in a precisely similar condition of internal crystallisation, and show precisely similar 

 phenomena. Whether these examples are specifically identical with L. conferta, 

 Lonsd., or belong to a distinct species, is a matter for further investigation. 



The type-species of the genus Labechia is the well-known L. conferta, Lonsd., 

 of the Wenlock Limestone. Another very interesting type, which I shall subse- 

 quently describe under the name of L. alveolaris, occurs in the Wenlock Limestone 

 of Britain. In the Devonian Limestone of Devonshire occurs another highly 

 remarkable form, which will be described as L. serotina (Fig. 4). The genus has 

 not hitherto been detected in the Ordovician (Lower Silurian) Rocks of either 

 Britain or Europe. At least two species, however, occur in rocks of this age in 

 North America, viz. L. Canadensis, Nich. and Mur., of the Trenton Limestone 

 (Plate II, fig. 3), and L. Ohioensis, n. sp., from the Cincinnati group of Ohio 

 (Plate II, figs. 1 and 2). The former of these types was taken by Dr. Murie and 

 myself as probably representing the ill-defined genus Stromatocerium, Hall (' Pal. 

 N. Y.,' vol. i, p. 48), and we based upon a microscopic investigation of its structure 

 an amended definition of this genus (' Journ. Linn. Soc.,' vol. xiv, p. 222). Further 



