90 TABULATE CORALS. 



with the larger and more oblique calices under the name of 

 varietas major (Brit. Foss. Cor., PL LXL, fig. 4 a). I thus 

 regret to find myself unable to adopt the opinion of my friend 

 Dr Lindstrom on this point, who regards the latter form (viz., 

 var. major) as the type of P. cristata, while he considers the 

 examples with the annular calices as specifically distinct. 



In a few instances, I have noticed the existence of an oper- 

 culum closing the mouth of a tube, but this seems to be un- 

 usual. The condition of the septa varies. In some examples 

 they cannot be recognised at all, whereas in others (certainly 

 not so commonly) the mouths of the corallites are seen to 

 be clearly marked by radiating ridges. Thin transverse and 

 tangential sections (PI. V., fig. i) show the same differences. 

 Usually such sections exhibit no traces of septa, or only a few 

 rudimentary tubercles, but sometimes there proceed tolerably 

 long spines into the interior of the tube. Similar spines are 

 present in most longitudinal sections, but in very varying num- 

 bers. Sometimes (PI. V., fig. i a} there are very few of them ; 

 but in other instances (PI. V., fig. i b) there are numerous 

 pointed spines which spring from the walls, and are directed 

 upwards into the visceral chamber. It seems almost certain 

 that these spines are truly septa, though some of them may 

 perhaps be of the nature of incomplete tabular. The tabulae 

 are well developed, about five or six in the space of two lines, 

 complete, usually curved, with their convexities turned towards 

 the base of the corallum, sometimes irregularly flexuous. I 

 have only been able to investigate the mural pores by means 

 of thin vertical sections, in which these openings may be often 

 partially detected. They are of no great size, and appear to 

 be either uniserial or irregular. 



P. cristata, E. and H., is distinguished from P. lamellicornis, 

 Lindst., by the different form of the corallum, the presence of 

 small calices interspersed among the larger ones, and the much 

 greater development of the tabulse. From the P. cervicornis, 

 De Blainv., of the Devonian, the present species is separated 

 by slight but upon the whole readily recognisable differences 



