GENERA OF FAVOSITID^E. 81 



the corallum, subpolygonal, rounded, or sometimes distinctly 

 oblique and semicircular, the margins being thick, and the 

 lower lip not specially prominent. Septa represented by minute 

 tubercles or spines, arranged in vertical rows (PI. IV., fig. 2 a). 

 Tabulae delicate, few in number, remote, and complete (PI. IV., 

 fig. 2 b). Mural pores few, irregular, of comparatively large size. 



Obs. Dr Lindstrom has kindly furnished me with speci- 

 mens of this, the type-species of the genus Pachypora, from 

 which I have been enabled to draw up the above description. 

 As the structure and affinities of the genus have already been 

 discussed at some length, it is unnecessary here to enter into 

 further details as to the characters of this interesting form. 

 In its general appearance it resembles most nearly a palmate 

 or dendroid Favosites; but the conspicuous thickening of the 

 mouths of the calices, and the consequent remoteness of these 

 apertures, is sufficient to separate it from the typical forms of the 

 latter. Sometimes the calices resemble those of Favosites in 

 being polygonal or rounded, sometimes they are like those of 

 Alveolites in being markedly oblique and semi-lunar; and both 

 these conditions are commonly present in the same specimen, 

 calices of the latter shape occurring principally towards the 

 ends of the branches. The lower lip of the calice is, however, 

 never markedly prominent, nor thinner than the rest of the cali- 

 cine margin. The nearest ally to P. lamellicornis is the P. 

 (Alveolites) Fischeri, Bill., of the Devonian of North America ; 

 but the corallum of the latter is invariably in the form of thin 

 lamellar or palmate expansions, never partially or completely 

 ramose, while the calices are commonly oblique and subtri- 

 angular over the whole surface. There is also a close resem- 

 blance between the present species and P. (Favosites) cristata, 

 E. and H., from the Upper Silurian of Britain ; but the latter 

 is always distinctly ramose, of more or less cylindrical branches, 

 while its tabulae are much more largely developed, and the 

 septa appear to be nearly obsolete. 



Formation and Locality. Upper Silurian (Wenlock Lime- 

 stone), Wisby, Gotland. (Coll. Dr Gustav Lindstrom.) 



