o/*Alecto and Aulopora. 127 



Some examples of this species are branched with tolerable 



rcguluvity, as in the specimen figured ; but others form com- 

 pressed and closely interlaced reticulations. No positive or 

 absolutely definite characters can be stated which would lead 

 to the reference of tiiis fossil to Aulopora rather than to Alecto. 

 Nevertheless the general aspect of the fossil is such that it 

 can almost positively be placed under the former genus. The 

 forms to which it presents the nearest alliance are A. JUiformisy 

 Billings, and A. (r) canadensis^ Nich., both of which are De- 

 vonian ; but it is readily distinguished from these, and l»y no 

 character more conspicuously than by the fact that tlie corallites 

 open in the axis of the branches, instead of making an angle 

 with the main stems. With a little care, also, there is no 

 great diflSculty in separating it from Alecto auloporoidesj to 

 which it presents a very considerable superficial resemblance. 



The examples oi Aulojiora arachnoidea described by Hall 

 are from the Trenton Limestone ; but ours are from a higher 

 horizon. The specimens which I have seen are all attached 

 parasitically to the surface of different species of C/uctetes 

 ( Mon ticu lipora) . 



Locality and Formation. — Cincinnati Group, Cincinnati 

 and Waynesville, Ohio. 



EXPIAXATION OF PLATE XI. 



Fiff. 1. Hippothoa injlata, Hall, sp., a small fragment, greatly enlarged. 



] a. Two of the cells of the same, still further enlarged. 

 Fiy. 2. Alecto auloporoides, Nich., a portion of the polyzoary gro^\-ing 



on Strophotnena alternata, greatly enlarged. 2 a. Portion of a 



branch of the same, still further enlar^d, showing the biserial 



cells. 2 h. Portion of another branch, in which the cells are 



uniserial below and biserial above. 

 Fig. 3. Alecto fromlosa. James, a reticulated example, of the natural size, 



growing on Strophomena alternata. 3 a. Portion of the same, 



enlarged. 3 b. Portion of the same, still further enlarged. 



3 c. Portion of the polyzoarv- of another specimen, enlarged. 



3 d. Portion of another specimen, enlarged, showing the minutely 



porous nature of the surface. 

 Fig. 4. Alecto confiisa, Nich., forming a crust on a crinoidal column, 



enlarged. 

 Fig. 5. Aulopora arachnoidea, Hall, a specimen in which the branching 



is regular and no close reticulation is formed, growing on 



Chcetetes gracilis, of the natural size and enlarged. 5 a. Portion 



of a branch of the same, greatly enlarged. 



