7 to NKW YOUK STATE MUSEUM 



the graptolites of the St Lawrence region. With these exceptions, these 

 extremely common fossil organisms of the graptolite shale remained com- 

 pletely unnoticed till Dr Gurley began systematically to study the North 

 American graptolites. He i-ecognized two species in the Beekmantown shales 

 of Point Levis, Quebec, both of which are found in the homotaxial Deep kill 

 beds. 



In one of them, D. t rid ens, its author observed- three denticles, 

 which, he states, " seem to indicate thecae, but from the extreme tenuity of the 

 film it is not possible to determine this point definitely." Our examples of the 

 same species show these same pointed denticles very distinctly in some 

 cases [pl.l7, fig.l9]. While they appear as nothing but incisions into the 

 margin of the fossil — which, however, by their regularity and sharp 

 delineation seem to refute the supposition that they could be a mere fring- 

 ing out of the margin due to the cleavage of the rock — we are able to 

 discern distinct, projecting thecae in several well preserved specimens of 

 the other species, D. monodon [fig,23]. They are also shown in profile 

 in a fragment of the apical part of the latter species and exhibit in the frontal 

 view trausversally oval apertures [pi. 17, fig.25]. 



These observations suggest that at least the two species of Dawsonia 

 noted in this place, Avere provided with a small number of thecae. The bodies 

 described here appear to represent the perfect organism, as they are clearly 

 and definitely bounded at both extremities. As colonies, they look very 

 different indeed from all other graptolite colonies, and they must, if they 

 should be proved by further investigations to be complete, be regarded as a 

 (|uite aberrant branch of the class of graptolites. 



The carbonaceous films, representing these two species of Dawsonia, 

 have, above all, the appearance of having originally belonged to bag-shaped 

 bodies. This impression is specially created by wrinkles which run parallel 

 to and increase toward the major margins [comp. fig.24:]. As these supposed 

 bags do not show any indications of attachment at either end, it is to 

 be inferred that the colonies remained free during their lifetime, and 

 the major poi-tion of the bags may have functioned as hydrostatic 

 apparatus. 



