18 Dr. H. A. Nicholson on some neio or 



marked septal ridges which surround the throat of the visceral 

 chambers in 8. Litineana; and its large corallites are deci- 

 dedly larger than is the case in the latter form. 



Horizon and Locality. Inferior Devonian, La Baconni^re, 

 Laval, Mayenne {coll. (Ehlert). 



A very nearly allied if not identical form occurs in the 

 Eifel ; but I have not yet fully examined this. 



Pachypora CEhlerti, Nich. 

 (PL I. figs. 2-2 c.) 



Spec. char. Corallum forming flat or slightly undulated 

 expansions, the under surface of which was doubtless originally 

 covered by an epitheca, though this is no longer recognizable, 

 and which vary in thickness from 2 millims. up to a centi- 

 metre. The upper surface exhibits the apertures of the calices 

 (PI. I. fig. 2 a) — which are very irregular in shape, but usually 

 exhibit two strong septal teeth, one on each side. Sometimes 

 there is only a single well-marked projection of this nature ; 

 sometimes there are three such ; but in any case the actual 

 mouths of the corallites are never regularly polygonal or 

 circular, or even crescentic, but are always to some extent 

 encroached upon by well-marked inward prolongations of the 

 wall, and their most general form is perhaps rudely quadran- 

 gular. Very commonly two or more of the calices run into 

 one another, and the calicine apertures thus become vermicu- 

 lar. The actual diameter of the tubes of the corallites varies 

 from one third to two thirds of a millimetre measured along 

 their greatest lengths ; but to that must be added the thickness 

 of the walls, so that in general about four calices are found in 

 a space of from 2 to 3 millims. The walls of the tubes, as 

 seen in tangential sections (PI. I. fig. 2 b), are very much 

 thickened ; but no lines of demarcation between adjoining 

 corallites can be made out. In thin vertical sections (PI. 1. 

 fig. 2 c) the same thickened condition of the walls and the 

 absence of any proper boundary between adjoining tubes can 

 be observed. Tabulae complete, but few in number and 

 irregularly developed. Mural pores not observed with cer- 

 tainty. 



Obs. This well-marked form seems to be a Pac}iyj)ora of 

 the general type of P. Fisclieri^ Bill., and P. frondosa, Nich., 

 though it possesses marked peculiarities of its own. Its 

 characters, in fact, increase the probability that it may be 

 ultimately necessary to still further subdivide the genus Pachy- 

 ipora^ Lindst., retaining this name for forms like P. lamelli- 

 cornis^ Lindst., P. Fischeri^ Bill., and their allies, and creating 

 a new genus, or subgenus, for such more natural and normal 

 types as P. cervicornisy Blainv., and P. cristata, E. & H. 



