EXPLANATION OF THE PLATES. 



by compression. Its upper margin is rounded at each side, and its lower part 

 has a deep turaulated indentation, which was evidently the entrance into the 

 stomach. This is the part mentioned in page 208. 



Fig. 1. c. Side view of the same, showing the remarkably flat form of the specimen, 

 from which peculiarity the specific name has been taken. The shelly crust of 

 the under side joins the upper at the sides. This is usually the case with tri- 

 lobites in this anterior portion of the animal. 



Fig. 2. Posterior part of the same species. 



PLATE XXVIII. 



Fossil corals of the genus Huronia, from Drummond Island, Lake Huron. 

 These corals are described in page 202. 



Fig. 1. Huronia Bigsbei. 



2. ■ vertebralis. 



3. turbinata. 



4. obliqua. 



5. spheroidalis. 



6. Section of H. vertebralis. 



The generic character of these corals is thus described by Mr. Stokes, who has given 

 them the above names : 



Polyparium stony, forming a straight jointed column of single cells placed 

 one over the other ; each joint having been in succession the habitation of the 

 living individual. The remarkable peculiarity which establishes these corals as 

 a particular genus is, that as a nevv generation arises, it forms its cell precisely 

 over the preceding one, covering its upper surface] entirely, and lengthening the 

 column of the coral by a new joint in a continuous line with those previously 

 formed. 



PLATE XXIX. 



Fossil corals from Drummond Island, Lake Huron. 



Figs. 1,2. a. 2. b. represent a species of Caryophyllia, remarkable for the tubes 

 proceeding from it, as describe<l in page 203. 



Fig. 3. Very small species of Turbinolia. 



Fig. 4. A species remarkable for the arrangement of the plates in the centre. 



Fig. 5. Another species of Turbinolia. 



Fig. 6. A species of Caryophyllia. 



