278 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



PiNACOTEVPA MARGINATA. (N . Sp.) 

 Plate 36, figs. 1, la & lb. 



Zoarium explanate, forming thin, flattened or flexuous, subcircular ex- 

 pansion,s, from three quarters of an inch to an inch in their maximum 

 diameter. Under surface covered with an extremely thin laminar epith- 

 eca : upper surface consisting of a broad central celluliferous area, sur- 

 rounded by a projecting lateral expansion of the epitheca, which is 

 entirely devoid of cells. Celluliferous area marked with large star-shaped 

 macula^, whose centres are about six mm. apart. Outei' and noncelluli- 

 ferous expansion variable in breadth, its upper surface marked by longi- 

 tudinal and nearly parallel raised lines of unequal size, which in some 

 specimens are interwoven with a few similar but concentric lines. Zocecia 

 (or autopores) at first recumbent but ultimately erect, very short, cylin- 

 drical, about a third of it millimetre broad at their summits, arranged in 

 subparallel lines which radiate from the macuhe, but very closely disposed, 

 and in some cases almost touching each other : orifices of the zocecia fre- 

 quently closed by flat opercula, and surrounded in each case by a thin, 

 slightly elevated and apparently granulose peristome. Interspaces very 

 narrow, occupied by a single series of polygonal interstitial cells or meso- 

 pores (over whose apertures a thin smooth calcareous membrane or " roof " 

 is usually stretched) except on the maculaj, where they are disposed in 

 small clusters. Lunarium nearly or quite obsolete. Microscopic sections 

 show that the interstitial cells or mesopores are comparatively large, and 

 placed one over the other, even in the macuhe, so as to form tabulated 

 tubes, and not vesicular tissue as in Fisttdij/ora. 



Lake Winnipegosis, at a small island on the south-east side of Dawson 

 Bay, J. B. Tyrrell, 1889 ; seven specimens. Also on a small island on the 

 east side of Lake Winnipegosis and east of the south end of Birch Island, 

 J. B. Tyrrell, 1889 ; two specimens, loose. 



This species is referred to Pinamfri/pa rather than to FiatnJipora or 

 LirJienalia, on the authority of Mr. E. O. Ulrich, who, in u, letter to the 

 present writer, dated 23rd September, 1891, makes the following remarks 

 on two of the best specimens collected by Mr. Tyrrell, which were sent 

 to him for examination : " This is a remarkable form which I think may 

 be safely described as a new species of Pinacotrijpa. The general expres- 

 sion of the surface is much as in several species of Fislidipora, but the 

 constant nummiform shape is distinctive. The chief peculiarity, however, 

 is the longitudinal .striation of the basal lamina. This is a very remark- 

 able feature, and one quite unknown to me. The cells are smaller and 

 the maculse more distinct than in 1'. degans, the Fistidipora elegmis of 

 Rominger." 



