222 Systematic Paleoxtolooy 



cf. Stromatopora hudsonica Dawson, 1879, Quart. Jour. Geol. Soc, vol. xxxv, 



p. 52, pi. iv, figs. 9a and 9b; pi. v, fig. 10. 

 cf. Stromatopora hudsonica Nicholson, 1891, Mon. Brit. Strom., p. 172. 

 cf. Stromatopora hudsonica Nicholson, 1891, Ann. and Mag. Nat. Hist., p. 312, 



pi. viii, figs. 1-3. 

 Stromatopora constellata Parks, 1908, Univ. Toronto Studies, Geol. Ser., 



No. 5, pp. 44-46. 



Description. — " Massive, hemisphoric, spheroidal or irregiilar ; com- 

 posed of thin concentric layers, which are penetrated by minute vertical 

 tubes or cells: surface of layers nodose, each elevation being marked by 

 an irregular stellate impression with undulating and bifurcating rays ; in- 

 termediate spaces smooth, or having only the rainvite cell apertures. This 

 species presents no important characters to distinguish it from the 8. con- 

 centrica, except the uneven surface of the laminae, and the stellate im- 

 pressions upon these elevations. The size of the minute cell is apparently 

 the same as in -S'. concentrica : and in such specimens as break only verti- 

 cally there is no positive means of distinguishing this .species beyond the 

 undulations of the laminag which correspond to the uneven surface. It 

 seems, indeed, probable that it may be only a variety of the S. concentrica, 

 presenting this peculiarity in its mode of growth." Hall, 18ol. 



The species is further described by Parks as follows: " Coenosteum 

 massive, hemispheric, spheroidal or irregular. The commonest type is 

 hemispheric, and in this form the species reaches a large size, possibly a 

 foot or more in diameter. Latilaminar structure distinct, but the latilam- 

 inae vary greatly in thickness. Exfoliation easy, presenting smooth or 

 gently undulating surfaces. Small, low, rounded mamelons may be present 

 or absent; when present they are situated about 5 min. apart. Small 

 astrorhizal systems appear on nearly all surfaces, even where no other 

 structure is observable ; they are very small — not more than 3 nun. in 

 diameter — and with very few branches. The spacing of these systems is 

 extremely variable — from 3 to G or 7 mm. As I have already stated, the 

 distribution of astrorhizte is of little or no diagnostic value, hi the 

 variety with mamelons, the astrorhizse generally coincide in position with 

 these eminences, but even this is not rigidly true. The skeletal matter 

 consists of radial pillars and concentric lamina:', which are intimately 



