290 Dr. G. J. Hinde — On Solenopora garwoodi, sp. nov. 



calcareous Algae. It is many years ago since this genus was recognized 

 in the Ordovician rocks in North America, Britain, and Russia; more 

 recently it was found in the Silurian rocks of the Isle of Gotland, 

 and in 1894 a species was described from the Jurassic rocks of 

 Gloucesteishire and Yorkshire. But until this fortunate discovery 

 of its occurrence in the Lower Carboniferous by Professor Garwood, 

 no example of the genus was known in any of the rocks between the 

 Silurian and the Jurassic. 



I am greatly indebted to Professor Garwood for permission to 

 describe this new and interesting species — which I propose to name 

 after him — and for providing me with numerous specimens and sections 

 for the purpose. 



Description. 



Form and Mode of Groivth. 



The thallus of this species grows in small, depressed, nodular 

 masses ; in their higher stages lobate extensions are produced, which 

 show a tendency to further division. The specimens measured are 

 from 20 to 26 mm. in diameter and about 14 ram. in height. It is 

 uncertain whether they were attached to other bodies or continued 

 free during their growth. They consist of very compact, hard lime- 

 stone, of a light greyish-brown tint, resembling that of the matrix in 

 which they are enclosed. In a horizontal section of a specimen which 

 has been figured (PI. X, Fig. 1) concentric lines or bands of a slightly 

 darker tint are seen at regular intervals extending across the thallus, 

 probably indicating periods of growth. 



Character and Arrangement of the Celh. 



Thin sections taken in a vertical or radial direction through the 

 thallus of this species sliow the cells with great clearness. Their 

 longitudinal walls are straight and even, but their transverse walls, 

 though sometimes straight, for the most part are slightly concave ; the 

 concavity is towards the upper or growing surface of the thallus 

 (PL X, Figs. 3, 6). The cells are closely arranged in vertical and 

 transverse rows, and the partition walls, under low magnification, 

 appear to be simple and imperforate. The vertical rows are generally 

 straight and parallel, but through the intercalation of fresh rows of 

 cells by growth they diverge slightly and have a fan-like appearance. 

 The transverse rows form concentric, evenly arched lines, extending 

 across the thallus. 



The cells vary considei'ably in size and form. Some are quadi'ate, 

 others oblong, and in others the length is much less than the width. 

 The cells in the same transverse row are usually of a corresponding 

 length or height, and it is frequently noticeable that a series of 

 concentric rows of fairly large cells is succeeded bj' a series of rows 

 of short cells, and this alternation may indicate periods when the 

 conditions were more or less favourable to the growth of the organism. 



Seen in cross-section the cells are closely fitted together, and their 

 outlines are very irregular ; some are entirely polygonal, whilst the 

 contours of others are partly polygonal and partly rounded (PI. X, 

 Figs. 4. 5, 7). 



