34 C. D. Walcott — Position of the Olenellus Fauna. 



worms or mollusks with much more propriety than to the 

 Algas. Specimens of . Cruziana, collected in Newfoundland, 

 lead me to think that it is a trail or burrow and not an Alga. 



No traces of land vegetation have been discovered in the 

 rocks of the Cambrian Period. 



Spongice. — The sponges of the Lower Cambrian are limited 

 to two genera, of which one, Protospongia, is found in the 

 upper beds of the Olenellus zone of the Atlantic Province, 

 and also in the Middle Cambrian in Nevada, NT ew Brunswick, 

 Newfoundland, Wales and Sweden. Leptomitus is confined to 

 the Lower Cambrian. 



Hydrozoa. — It is to the researches of Dr. A. G. Natkorst 

 that we owe a knowledge of the occurrence of Medusae in the 

 Lower Cambrian rocks of Sweden. By a series of compari- 

 sons between the casts found in the rocks at Lugnas and the 

 casts made by the impressions of recent Medusas, more espe- 

 cially of Aurelia aurita and Cyrena capillata, he has shown 

 that it is extremely probable, if not certain, that the delicately 

 constructed Medusas lived during the Lower Cambrian epoch 

 and left traces of their existence in the clays and sands of the 

 seashore. Dr. JSTathorst figures and describes* Medusites Lind- 

 stromi Linnrs., M.favosus Nathorst and M. radiata Linnrs., 

 and states that he thinks the so-called species of Eophyton are 

 the casts of trails made by the Medusas in moving along the 

 sea bed. 



There are, in the collections of the United States Geological 

 Survey, a group of forms from the middle part of the Cambrian 

 in Alabama, that appear to be generically related to Medusites 

 Lindsti^omi. They will be described with the description of 

 the Middle and Upper Cambrian fauna. In ascending the 

 geological series, it is not until the lithographic slate of the 

 Upper Jura, at Solenhofen, etc., is reached, that traces of the 

 Medusas are again met with. 



The Graptolitidas are represented by two sj)ecies that are pro- 

 visionally referred to the genera Phyllograptus and Climaco- 

 graptus. These generic types are not met with again until the 

 base of the Ordovician is reached, where they are largely devel- 

 oped. Mr. Matthew has described two species of graptolites 

 from the Middle Cambrian of New Brunswick, which he refers 

 to Dendrograptus and Protograptus. 



Actinozoa. — It has been an open question for some years 

 whether the forms referred to the genus Archasocyathus were 

 corals or sponges. Dr. G. J. Hinde has recently reviewed the 

 genera and species, and concluded that they form a special family 

 of the Zoantharia sclerodermata, in some features allied to the 



* Kongl. Svenska Yetenskaps-Akademiens Handlmgar, Bandet 19, N. 1, 1881. 

 Om Aftiyck af Medusor i Sveriges Kainbriska Lager. 



