FOSSIL JELLY FISHES FROM THE MIDDLE CAMBKIAN 



TERRANE. 



By Charles D. Walcott, 



Honorary Curator of ike Department of Paleontology. 



During the past iiiue years large collections of fossils have been made 

 from the Middle Cambrian shales and limestones of the Coosa Valley, 

 Alabama. At two horizons silicions concretions occur in the fossilifer- 

 ous shale and, associated with them, what have locally been known as 

 " star cobbles." Some of the latter suggest the sea-urchin, and others 

 that are spread out on flat nodules resemble starfish. It was not until 

 1893 that I felt assured that the so-called '' star cobbles" were fossil 

 MedusjTB. There are now more than 8,000 specimens in the collections 

 of the Ignited States Geological Surve5^ From this ample material two 

 types have been separated that are allied to the recent Discomedusic. 



Numerous fragments of trilobites, etc., of Middle Cambrian age occur 

 in the shale, and they are also attached to and embedded in many of 

 the flattened nodules, and more rarely attached to specimens of the 

 jVIedusie, From the large number of sjjecimens that have been found 

 over a relatively small area, it is evident that they were gregarious and 

 very much like the modern Rhizostome {Polydonia frondosa) in their 

 habits. 



Two genera and three species have been recognized, namely: BrooJc- 

 sella, new genus, B. aJternafa, new species, B. eonfuaa, new species, 

 Laotira, new genus, and L. cambria, new species. 



These forms, with Bactyloiditcs asteroides of the Lower Cambrian, may 

 be grouped together in the family Brooksellida". 



Family BKOOKSELLID.E. 



Discomedusa* with a lobate umbrella; without tentacles and central 

 oral opening in the adult; with a radial canal in each lobe of theexum- 

 brella, and a central stomach ; oral arms central or represented by 

 interradial arms or lobes attached to the central axis or to the sub- 

 umbrella surface; reproduction sexual or by fission. 



The following genera are included in the family: Brooksella, Laotira, 

 and Bactyloidites. 



BROOKSELLA, new genus. 



Discomedusa" with a lobate umbrella, G, 7, to 12 or more lobes ; with- 

 out tentacles and without ( ?) central oral opening; with a simple radial 



Proceedings of tlic I'uited States National Mn.seuiii, Vol. XVIII — No, 1086. 



611 



