622 E. ETHEKIDGE ON THE PALAEONTOLOGY OE THE 



the parallelogrammic fenestrates with rounded angles, the striated 

 reverse, and with it all a somewhat irregular appearance. If my 

 reference to Prof, de Koninck's form is correct, it will necessitate the 

 transference of the species from the genus Fenestella to Polypora ; for 

 although the state of preservation is not good, still there is quite 

 enough evidence to show that it is a Polypora, possessing the above 

 characters in common with F. megastoma, De Kon. ; and it must be 

 borne in mind that the celluliferous face of the latter was unknown 

 to Prof, de Koninek. 



Yery closely approaching to P. megastoma, De Kon., is one of 

 Dr. Geinitz's figures * of P. marginata, M'Coy ; but I am sorry that 

 I cannot agree with so eminent an authority as Dr. Geinitz in his 

 reference of the Nebraska forms to M'Coy's species ; for the figures 

 in question do not appear to me to agree with M'Coy's description 

 at all. 



Log. Peilden Isthmus, lat. 82° 43'. 



Polypoka biaemica, Keyserling. (PI. XXYIII. fig. 4.) 



Polypora biarmica, Keyserling, Peise in das Petschora-Land, 1846, 

 p. 191, t. 3. f. 10 ; Geinitz, Dyas, 1861, p. 117 ; Gein. Carbonforma- 

 tion u. Dyas in Nebraska, 1861, p. 68, t. 5. f. 13 ; Prout, Trans. 

 St. Louis Acad. i. p. 450 ; Toula, Sitz. k. Akad. d. Wissensch. zu 

 Wien, 1875, lxxi. p. 562, t. 3. f. 15, a-c ; Miller, American Pal. Foss. 

 1877, p. 99. 



P. spindet, Meek, Hayden's Pinal Report Geol. Survey of Nebraska, 

 1872, p. 155, t. 7. f. 6. 



Sjp. char. Polyzoarium widely funnel-shaped, expanding; inter- 

 stices strong and robust, often bifurcating, as broad as, or broader than 

 the fenestrules, and nearly flat on the celluliferous or obverse face, of 

 less breadth on the reverse and more convex; dissepiments short 

 and narrow on the obverse, sometimes becoming almost lost, but on 

 the reverse they are longer and wider and on the same level with 

 the interstices, whilst on the obverse they are somewhat below the 

 latter; fenestrules variable in outline on the obverse, funnel-shaped, 

 increasing in breadth towards the reverse, where they are, as a rule, 

 quite circular or sometimes a little elongated; on the obverse the 

 fenestrules are, as a rule, very narrow and sometimes quite slit-like, 

 but always with the sides indented by the apertures of the cells : 

 apertures of the cells circular, arranged in oblique rows on the in- 

 terstices and devoid of projecting or prominent margins ; the normal 

 number in each row is three, sometimes four, and immediately 

 before bifurcation of the stem takes place the enlarged dissepiment 

 may carry six. 



Obs. The form which I have assumed to be P. biarmica, Key- 

 serling, is a most interesting one, from the peculiar change the 

 polyzoarium appears to undergo with age and increased growth. 

 The obverse and reverse differ so materially in appearance that they 

 might easily be mistaken for distinct species, were it not for 



* Oarbonformation und Dyas in Nebraska, t. 5. f . 2. 



