AET. 14 MICHIGAN TRAVERSE GROUP POHL, 21 



correlation purposes with biological relatives found elsewhere. The 

 present section will therefore deal only with the general phases of 

 the subject being limited to a discussion of those distinctive species 

 known to have a restricted occurrence within one or another of the 

 three stratigraphic units of the Little Traverse Bay district. 

 Throughout the sequence fossil remains are legion, but fortunately 

 for stratigraphic discrimination a number of species and several 

 genera have, as usual, a limited range in the succession, and may 

 thus be used as criteria for a ready and undeniable determination 

 of exposed portions of the section. 



Indications of the existence of sponges in the Traverse are rare, 

 and yet in several beds numerous, long, monaxon spicules of an uni- 

 dentifiable Silicisponge are found. The most notable of these occur- 

 rences is at the top of the section at locality 21 (middle Petoskey). 



No attempt will be made here to give the ranges and restrictions of 

 the numerous species of the Hydrocorallines, algae, and sponges 

 included under the general term '•'■Stromatopora.'''' Several of them 

 have been described but they have never been studied in regard to 

 their stratigraphic position. 



From a stratigraphic and biologic standpoint the best understood 

 organic remains of the Traverse series are the corals. This is due 

 to the work of Grabau, and from his unpublished manuscript (1915), 

 is derived the following summary of the positions occupied by a 

 number of closely discriminated species. So far as is now known the 

 species cited for the various units are restricted to them respectively. 



Petoskey formation : 



Stereolastna cf. recta (Hall). 



Heterophre litis cf. prolifica (Billings). 



Pinnatophi/lluiii scyphus (Rominger). 



P. scyplius carinatus Grabau (cliironym). 



Cyailiopliyllum rotustutn Hall. 



C. subrobusttim Grabau (ebironym). 



Meropliyllum kegomiffense Grabau (chironym). 



Prist iphifUum longiseptum Grabau (chironym). 



Cylindrophyllum panictmi (Winchell). 



C. magnum Grabau (chironym). 



Cystiphyllum cf. vesiculosuin (Goldfuss). 



C. conifollis Hall, 



0. varians Hall. 



C. aggrcgatum Billings and aggregaium, caespitosum, Schluter. 



Aulopora serpens Goldfuss. 



Ceratopora cf. jaeksoni Grabau. 



Syringopora crassata Winchell. 



Favosites transitoritis Grabau (chironym). 



F. alpenensis dumosus "Winchell, 

 Charlevoix stage: 



Heterophyllum alpenense Grabau (chironym). 



Pachypora lim;itaris (Rominger). 



