CORALS OF THE CINCINNATI GROUP. 217 



Some examples of this species are branched with tolerable regularity, 

 as in the specimen figured; but others form very confused and closely 

 interlaced reticulations. No positive or absolutely definite characters 

 can be stated which would lead to the reference of this fossil to Aulopora 

 rather than to Alecto. Nevertheless, the general aspect of the fossil is 

 such that it can almost positively be placed in the former genus. The 

 forms to which it presents the nearest resemblance are A. filiformis, Bil- 

 lings, and A. (?) Canadensis, Nich., both of which are Devonian; but it 

 is readily distinguished from these, and by no character more conspic- 

 uously than by the fact that the corallites open in the axis of the 

 branches, instead of forming an angle with the main stem. With a little 

 care, there is also no great difficulty in separating it from Alecto aulopo- 

 roides, Nich., to which it bears a considerable superficial resemblance. 



The examples of Aulopora arachnoidea described by Hall are from the 

 Trenton limestone, but our examples are from the horizon of the Hudson 

 River group. The specimens which I have seen are attached to the ex- 

 terior of different ramose species of Chsetetes. 



Position and locality : Cincinnati group, Cincinnati, Ohio. From the collections of 

 Mr. U. P. James and Prof. Edward Orton. 



Genus STEEPTELASMA, Hall, 1847. 



(Pal. N. Y., Vol. I., p. 17.) 



Corallum simple, turbinate, free ; epitheca well developed ; septa well 

 developed, more or less twisted and united with one another towards the 

 center of the visceral chamber, where they sometimes form a species of 

 vesicular tissue. No columella, nor any dissepiments. Tabulse remote, 

 irregular, and poorly developed. A single septal fossette. 



This genus stands in a somewhat dubious position ; but I see at pres- 

 ent no option but to retain it, if S. corniculum is to be taken as the type 

 of the genus. The badly characterized genus Petraia, Munst., is stated to 

 possess no tabulse ; otherwise Streptelasma would certainly^have to be re- 

 garded as a synonym of this, as has already been done by McCoy and 

 Billings. On the other hand, Milne Edwards and Haime (Brit. Foss. 

 Corals, Introduction, p. 68) state that Streptelasma is separated from Cy- 

 athophyllum by the fact that the wall is " destitute of an epitheca and 

 covered by sub-lamellar costse." This I do not comprehend, as the many 

 specimens of S. corniculum which have come under my notice have the 

 epitheca remarkably well developed, except when they have been much 



