GENERA OF FAVOSITIDyE. 



99 



pores, of well-developed though sparse tabulae, and, sometimes 

 at any rate, of splniform septa. On the other hand, the corallites 

 exhibit, in an even more extreme degree, the thickening of 

 their walls by a secondary concentrically-laminated deposit of 

 sclerenchyma, which is so characteristic of Pachypora, Lindst. 

 There is, indeed, no feature in the way of internal construc- 

 tion which could be brought forward as separating Striatopora 

 from Pachypora ; and in distinguishing these two types we 

 have to fall back upon a well-marked external character. In 

 all the forms of Pachypoj^a, Lindst., namely, the actual orifices 

 of the corallites are but slightly sunk beneath the general sur- 

 face, and they are surrounded by thick and but faintly-crested 

 margins. On the other hand, in all the species of Striatopora, 

 Hall, the circular apertures of the corallites are more or less 

 deeply sunk below the general surface, and open at the bottom 

 of an expanded polygonal cup (fig. i8), the actual margins of 

 which are as thin as the lips of the calices in a species of 

 Favosites. This feature is quite sufficient to distinguish Striato- 

 pora from either Favosites or Pachypora, between which it is in 

 this respect an intermediate link ; though it must be admitted 

 that the filling up of the cup-like terminations of the corallites 

 by the matrix to the level of their free margins, sometimes 

 renders it difficult to apply this distinction in practice. More- 

 over, the floor of the cup-shaped calices of Striatopora is seen 

 in perfect specimens to be generally striated in a radiating 

 manner, with delicate ridges or rows of tubercles, representing 

 septa (fig. 1 8) ; though this character also cannot be constantly 

 recognised, and is present in a minor degree in some forms of 

 Pachypora {e.g., P. cristata, E. and H.) 



The geological range of Striatopora, so far as known, is a 

 limited one, all the described species being either Upper Silu- 

 rian or Devonian in age. I. have made a careful microscopic 

 examination of 5. Linneana, Bill., from the Hamilton group 

 of Ontario, and also of S. Haiti, Lindst., from the Wenlock 

 Limestone of Gotland, but I shall merely give a brief descrip- 

 tion of the former of these. So far as I am aware, the genus 



