iw.'perfecily -known Species of Stromatoporoids. 3 



rows. On the other hand, tangential sections (PI. I. fig. 2) 

 show the cut ends of the isolated and imperfect radial pillars 

 along with the irregularly divided edges of the concentric 

 Jaminge. Tangential sections also show no traces of radiatino- 

 " arms " springing from the radial pillars. Small astrorhizte 

 are seen in tangential sections, and these usually have a wall- 

 less central canal ; but the openings of the latter on the surface 

 are riot prominently elevated. 



C. vesiculosiaii *, Nich. & Mur., belongs to a series of forms 

 the specific determination of which is exceptionally difficult. 

 The forms in question, viz. C. vesiculosum, Nich. & Mur., C. 

 variolare^ Rosen, C. Linnarssoai, Nich., and C. crassum, 

 Nich., are all easily recognized as distinct when typical 

 examples are selected for examination. It is therefore expe- 

 dient to distinguish them by separate specific names. At the 

 same time there are close relationships between all these forms, 

 and examples are not uncommon which show intermediate 

 characters, and which therefore it is difficult to refer definitely 

 to any one of the four. In a less striking form a passage may 

 also be traced between this group of types and G. fastigiatiim, 

 Nich. 



From the forms above mentioned C. vesiculosum is best 

 distinguished by the extreme closeness with which the con- 

 centric laminae are set and the resulting minuteness of the 

 cells which compose the coenosteum. Not only are the laminae 

 exceedingly close, but the interlaminar spaces are nearly 

 equal in width, and the cellular tissue of the skeleton is 

 thus approximately uniform. On the other hand, in typical 

 examples of C. variolare, Kos., the interlaminar spaces are 

 unequal in size — wide spaces alternating tolerably regularly 

 with spaces which are much narrower than the average and 

 which are usually arranged in groups (PI. I. fig. 5). In G. 

 Linnarssoni, Nich., again, the concentric lamina? are much 

 less crumpled, and the cells of the interlaminar spaces are 



* From a recent paper by Dr. Rominger (Proc. Acad. Nat. Sci. Pliil. 

 188G) I gather that this observer had given the name of Stromatopora 

 minuta to the present species many years ago (1871) in a memoir in which 

 a number of Stromatoporoids were described and named. As the memoir 

 in question, however, was never published (and is still unpublished), this 

 name has, of coiu'se, no validity. The same observation applies to a 

 number of additional names given by Dr. Kominger in the same memoir 

 to various Stromatoporoids, which have been subsequently described and 

 named by other authorities. As the non-publication of the memoir in 

 which these names were originally given deprives the same of all force 

 as against names published prior to 1886, it is not altogether easy to see 

 the object gained by the reproduction of these MS. titles at the present 

 day. 



1* 



