SUB-GENUS DIFLOTRYPA. i6i 



Corallites directed upwards nearly at right angles to the entire 

 basal plate, and opening upon the upper aspect of the colony. 

 Surface with scattered and very slightly raised " monticules " 

 composed of corallites slightly above the average in size. 

 Corallites of two principal kinds, large and small, the tubes of 

 both series interminoled throucjhout the entire corallum. Larore 

 tubes, mostly from i-iooth to i-6oth inch in diameter, more or 

 less thin-walled, angular or sub-angular, often hexagonal, in 

 shape, and sometimes arranged in small groups or rosettes of 

 four or five tubes each. Small corallites very numerous and 

 very variable in size and form, but always thin-walled and 

 angular, and wedged into all the interspaces left between the 

 large tubes. Along with the ordinary small corallites there 

 exists a variable number of thick-walled spiniform corallites, or 

 hollow spines, distributed here and there at the angles of junc- 

 tion of the thin- walled tubes. In internal structure all the 

 tubes (except the spiniform ones) are equally thin-walled, but 

 the large corallites are crossed by remote horizontal and com- 

 plete tabular, while the intermediate smaller corallites are tra- 

 versed by tabular of the same type, but much more closely 

 set. 



Obs. — In the description of this species which I gave in my 

 recently published work on the ' Palaeozoic Tabulate Corals ' 

 {loc. cit. supra), I fell into a curious and unlucky mistake, which 

 led to my drawing up of my diagnosis from specimens really 

 referable to two quite distinct forms. My collection from the 

 Trenton Limestone of Peterboro', Ontario, included, namely, 

 a number of discoid specimens of a Montictdipora which (being 

 from the same formation and locality) I concluded to belong 

 to a single species, since they presented no special external 

 features to separate them. I made thin sections ^ of two or 

 three of these, without taking special care that the sections 



^ The sections now alluded to were made by me some years ago, and the error 

 which resulted from their intermixture not only remained undetected by me until 

 the last three or four months, but was actually published as long ago as 1876 (see 

 " Notes on the Palteozoic Corals of the State of Ohio," Ann. and Mag. Nat. Hist., 

 sen 4, vol. xviii. p. 88, PI. V. figs. 6, 6(?). 



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