Reviews — Professor G. Lindstrbm on Heliolitidce. 271 



where there are outcrops of Silurian and Devonian rocks. They are 

 more especially abundant in Northern regions both of Europe and 

 America, and the most prolific locality is the Isle of Gotland, from 

 which place Lindstroin enumerates thirty species and varieties, out 

 of a total of forty-six described in this memoir. Only eleven species 

 occur in British rocks, and sis or seven forms have been recognized 

 in Australia. 



According to the author, there is very great difiSculty in defining 

 the limits of species in the HeliolitidEe, since even in the corallites of 

 the same compound stock there is a considerable amount of variation 

 in their dimensions, their distance from each other, and the amount 

 of the coeaenchyma between them, but he finds that the shape and 

 size of the septa, the nature of the coenenchyma and dissepiments, 

 and, subordinately, the mode of growth, are of more systematic 

 value. 



Lindstrom considers that the coenenchyma is the most prominent 

 general feature in the Heliolitidas, and in this and the allied family 

 of the CoccoseridEe four kinds of it are distinguished: (1) tubular, 

 consisting of narrow polygonal tubes divided by regular horizontal 

 tabulae, as in Heliolites ; (2) vesicular, of thin convex lamellae, as 

 in Propora, E. & H. ; (3) bacular, of solid vertical rods or haculi, 

 as shown in the Coccoseridse ; and (4) compact, composed of a 

 dense, somewhat granular, homogeneous mass, showing longitudinal 

 lines, the traces of filled-up tubuli. This occurs in Pycnolitlius, 

 gen. nov. 



Considerable discussion has taken place with respect to the 

 nature of the coenenchyma in Heliolites and its allied genera, and the 

 author gives an account of its early stages and manner of develop- 

 ment. It is seen growing on the lower edge of the calicle of a 

 primary or initial cornet-shaped polypierite, not more than 0'6 mm. 

 in length and width, and may be developed either from one side of 

 this initial form or all around a calicle, which, by rising as a tube 

 above the parent coenenchyma, introduces the intracalicinar gemma- 

 tion, and thus for a time exists as a portion of a solitary individual. 

 Lindstrom supports the view that the coenenchyma of the Heliolitidse 

 is an endothecal structure, although no exterior theca for every single 

 polypierite in a compound coral is developed, and, strictly con- 

 sidered, that it forms an integral part of every calicle in the 

 compound coral. 



Nicholson and Moseley, on the other hand, regarded the corallum 

 in Heliolites as tenanted by two kinds of polypes : one kind, fully 

 developed, inhabiting the septal calicos (autopores) ; and the other, 

 rudimentary form, occupying the surrounding tabulated tubes 

 (siphonopores), which, therefore, were not coenenchymal in character. 

 .It must be acknowledged that there are some facts tending to support 

 the view, still held by some recent writers, that the siphonopores 

 (coenenchymal tubes) in Heliolites were occupied by zooids. Thus, 

 for example, Nicholson ^ records the fact that in Heliolites duhius, 

 Fr. Schmidt, a single siphonopore may sometimes be observed to be 



1 Man. Pal., vol. i (1889), p. 337. 



