SUB-GENUS MONOTRYPA. 179 



I have examined, the tubes seem to radiate from a point 

 near the base; but Mr Ulrich describes the normal arrange- 

 ment to be that the tubes " radiate from various centres, which 

 correspond in number to that of the prominent nodules ob- 

 served on the surface." This observer also states that, after 

 examining transparent sections, he had been unable to detect 

 any tabulae ; and this observation is so far correct that tabulae 

 are certainly totally wanting throughout a great part of the 

 corallum. I find, however, that there is commonly a single 

 tabula (sometimes two or three) developed in many of the 

 tubes at a short distance inwards from their termination on 

 the surface, and that these tabulae are commonly placed at 

 corresponding levels in contiguous tubes. An occasional 

 tabula may also be observed in the interior of the corallum. 



M. ii^rcgtilaris, Ulrich, is most nearly allied in internal 

 structure to the smaller types of AL tmdulata, Nich. (which 

 may possibly constitute a separate species), but it is suffici- 

 ently distinguished by its external characters, and its much 

 more limited development of tabulae. 



Horiso7t and Locality. — Cincinnati Group, Ohio (according 

 to Ulrich, it marks an horizon of about 550 feet above low- 

 water mark in the Ohio River, Cincinnati). 



Monticulipora (Monotrypa) quadrata, Rominger. 



(Fig. 36.) 



Chcetetcs quadratus, Rominger, Proc. Acad. Nat. Sci. Phil., 1866, p. 115. 

 ,, rhombicus, Nicholson, Quart. Journ. Geol. Soc, vol. xxx. p. 507, 



PI. XXIX. figs, ii-ii/^, 1874. Pal. Ohio, vol. ii. p. 201, PI. 



XXI. figs. 12, 12^, 1875. Ann. Nat. Hist., ser. 4, vol. xviii. 



p. 86, PI. V. figs, i-i/;, 1876. 

 {Non Diannlifcs rJiombicus, Dybowski, Die Ch^etetiden, p. 33, 1877.) 



Spec. Char. — Corallum dendroid, of cylindrical or sub- 

 cylindrical branches, which vary from rather more than two 

 up to five lines in diameter, and often terminate in rounded 

 or bulbous extremities. Corallites primitively thin - walled, 



