HAMILTON CEMENT ROCK. 397 



Rhynchodus excavatus. NevVberry. 



Tooth small, when entire, perhaps two and a half inches long by 

 one and a quarter inches deep; crown alone preserved. Of this, the 

 external surface is marked vertically with vermicular furrows; supe- 

 rior margin sinuous, terminating anteriorly in a prominent point; the 

 superior surface irregularly excavated and roughened, showing two 

 prominent points, or tubercles, one on the middle of the exterior 

 margin, the other on the inner margin, and near the anterior ex- 

 tremity. The inner surface of the tooth shows a prominent ridge, 

 running up to the anterior point. This tooth is evidently fitted for 

 trituration rather than cutting, and resembles, in its general form, B. 

 frangons of the Corniferous limestone. It is, however, much smaller 

 and thinner, and the tubercles of the upper surface are differently 

 situated from what they are in the tooth of that species. 



Locality and Formation. Hamilton Group. Brown Deer, Mil- 

 waukee county, Wisconsin. 



In addition to the fish remains, there are the following inverte- 

 brates: Of Bryozoans, a Fenestella and a tuberculated Trematopora 

 occurring in massive and f rondose forms ; of Corals, the cast of the 

 cup of a CyatJiojphyllum; of Brachiopoda, a new species of Lingula, 

 and also one of Disoina, Orthis impressa, and an undetermined 

 Orthis, Strophodonta demissa, S.perplana, Chonetes coron<ita and a 

 species closely resembling C. d&flecta, a Froductella, allied to P. 

 spinuUcosta, Spirifera mueronata, 8. medialis, S. granuUfera, 8. 

 fornacula, 8. pinnata, a species allied to 8. fornacula, but larger 

 and one near 8. angusta, 8piriferina zigzag, Cyrtina Hamiltonensis, 

 Trematospira Mrsuta, Atrypa reticularis, A. ooddentali^, Le%or- 

 hynchus, resembling Z. Kelloggi; of Lamellibranchs, a Fteronites, 

 FalcBoneilo constricta, F. emarginata, a species allied to F. plana, 

 Modiomorpha concentrica, and an undetermined species; of Pter- 

 opods, an Ecculiomphalus, closely resembling Euomphalus laxus; of 

 Cephalopods, two new species of Gomphoceras, and an Orthoceras; 

 and of Crustaceans, Fhacops rana. 



These show a preponderance of Hamilton forms, some of which are 

 ■highly characteristic species, and occur in great abundance. With 

 these are mingled a number of Corniferous species, representing a 

 lower horizon, and a few Chemung forms belonging to a higher 



series. 



Age. The foregoing fossils are entirely decisive as to the age of 

 the formation, and place it in the early portion of the Hamilton 

 period. This is entirely in harmony with its stratigraphical relations 

 and with the general geological structure of the interior of the conti- 



