272 Revieics — Professor G, Lindstroni on Heliolitidce. 



developed vertically and directly into an autopore. This observation 

 has been confirmed by Gardeson, and Lindstrom also states that the 

 narrow tubuli of the coenenchyma in this species by-and-bye expand 

 or widen and are changed into real calicles (p. 71). A similar 

 metamorphosis of a coenenchymal tube into a true calicle by 

 a gradual increase in width and the development of septal spines, 

 likewise occurs in HeUoUtes hirsutus, Linds., sp. nov. 



With regard to those genera in which the coenenchyma is without 

 tubuli, and consists of vesicular tissue with solid spines or rods, or of 

 a compact sclerenchyma, the question of dimorphism can hardly arise. 



In favourably preserved specimens, the structure of the thecal 

 walls and the septa in the Heliolitidee can be seen to consist of 

 minute microscopic fibres radiating upwards and inwards from 

 a median dark line (whitish by reflected light), the same as in most 

 other corals. The septa in Heliolites are thin laminse, sometimes 

 with spiny margins ; in the Plasmoporinse they are reduced to 

 a series of spines which spring from narrow longitudinal ridges 

 within the calicle. Their degree of development varies much in the 

 same stock, and in some instances they appear to be altogether 

 wanting. There are twelve septa in the normal calicle, and this 

 number is very constant throughout the group. There can be no 

 doubt of the true nature of the septa in the Heliolitid^, and they are 

 entirely distinct in character from the pseudosepta in Heliopora, with 

 which they have wrongly been compared. Three modes of increase 

 have been observed : by coenenchymal, intracalicinal, and epithecal 

 or coenothecal gemmation. As a general feature, Lindstrom has 

 noticed that some of the earlier species are characterized by closely 

 placed calicles and slight development of ccenenchyma, which may 

 perhaps indicate a descent from ancestoi's without ccenenchyma. In 

 Lower Silurian (Ordovician) strata the predominant tj-^pes belong to 

 the Plasmoporinae and the allied Coccoseridas (these latter are con- 

 fined mainly to the lower horizon) ; whilst the Heliolitinee proper 

 flourished principally in the Upper Silurian. 



As the chief distinguishing features of the Heliolitidae and the 

 allied Coccoseridae, the author states that the individual polypierites 

 are composed of an interior area enclosed within an inner theca, 

 vsrith twelve regular septa, and of an exterior area without any 

 separating wall for each polypierite, and forming a diff"erently 

 shaped coenenchyma. 



Lindstrom subdivides the Heliolitidse into three tribes, mainly 

 according to the nature of the coenenchyma : (1) Heliolitinidee, with 

 lamellar septa and coenenchyma of polygonal tubes ; (2) Plasmo- 

 porinse, theca thick, coenenchyma vesicular ; and (3) Pycnolithinse, 

 with dense, compact, granular coenenchyma. 



The subfamily Coccoseridge is characterized by short thick septa, 

 the central area of the calicle is filled with columnar bacilli which 

 project as papillaa on its flooi', the coenenchyma is bacular, tubes 

 when present are narrow with a few tabula3. In this sub-group the 

 following three genera are included : Coccoseris, Eichwald, Protaraa, 

 E. & H., and AcanthoUthus, Linds., gen. nov. 



