TERRIBLE FISHES AND THEIR COMPANIONS. 181 



be a small cylindrical wall running down along the length of 

 the coral tube. Within this sinks a pit abruptly an eighth of 

 an inch. Really, however, there is no true inner wall. From 

 this apparent wall regular radial lines run to the outer wall. 

 These are the upper edges of vertical radiating plates called 

 septa, which extend the whole length of the coral tube. These 

 forms are beautiful enough without polishing. Still, certain 

 internal structures are by polishing, brought out with admir- 

 able clearness and beauty. For instance, if the cake is split 

 vertically and one surface polished, you see that the space be- 

 tween each two septa is divided from end to end by delicate 

 horizontal dissepiments, giving the whole polished surface the 

 appearance of a piece of very fine woven cloth. The dealers 

 in these specimens give them various names, some of which 

 are quite absurd. The scientific name of this species is A-cer- 

 vu-la'-ri-a Da-vid-so'-ni. The first word signifies a little hillock 

 or cake; the second, means Davidson's; and we might call it 

 "Davidson's coral-cake." This Davidson was a very distin- 

 guished English writer on fossil Brachiopods. It would not 

 be a great hardship for visitors to Petoskey to learn to call 

 this coral by its correct name. 



This species is found in America nowhere except in the 

 Hamilton Group, which you will remember, runs into the 

 Corniferous Limestone. It is found nowhere in the world in 

 such beauty and abundance as on the south shore of Little 

 Traverse Bay. The perfect specimens occur imbedded in soft 

 blue clay forming beds ten or twelve inches thick between 

 sheets of solid limestone. One can extract them with the 

 naked hand. By Drift action these coral cakes have been 

 transported like bowlders, from the northern part of the state 

 all over the southern part. The same coral is found also near 

 Iowa City and sparingly at other localities. 



There is another fine coral found on the shore of Little 

 Traverse Bay, which has been named Fav-o-si'-tes Al-pe-nen'-sis, 

 which means the " Alpena Favosite." Alpena is at the head 

 of Thunder Bay on the east shore of the state, and this coral 

 occurs very abundantly, also, in that region. It is shaped 



