NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. 155 



Sub-Class Merostomata 



Order Aglaspina, new order 

 Family Aglaspidse Clarke 



Genus Molaria, new genus 



Genus Habelia, new genus 



Genus Emeraldella, new genus 

 Order Limulava Walcott 

 Family Sidneyidse Walcott 



Genus Sidneyia Walcott 



STRATIGRAPHIC DISTRIBUTION 



The several genera of the four subclasses (with the exception of 

 the group of malacostracans represented by genera other than 

 Hymenocaris and the trilobitic genera MolHsonia and Tontoia) have 

 approximately the known vertical range in the Cambrian noted in 

 the diagram on page 156. 



In addition to representatives of the subclasses Branchiopoda, 

 Malacostraca, Trilobita, and Merostomata, mentioned in this paper, 

 I have added in the table genera of the Merostomata that occur in the 

 Lower Cambrian and Algonkian, respectively, and of the Ostracoda 

 in the Lower Cambrian, in order to present an outline of the lowest 

 known stratigraphic position of the five subclasses of Crustacea. 

 With the exception of the Branchiopoda all of these are known to 

 have representatives in later Paleozoic formations. 



The subclass Merostomata is represented by Beltina^ in the pre- 

 Cambrian ; by Amiella ^ in the upper part of the Lower Cambrian, by 

 the latter genus and Habelia, Molaria, Emeraldella, and Sidneyia '' 

 in the Middle Cambrian Burgess shale; and by Aglaspis* and 

 Strabops ° in the Upper Cambrian. 



The Phyllocarida is first known in the Lower Cambrian by 

 Isoxys^ a genus that is represented in the Burgess shale. Hymeno- 

 caris is well distributed in the lower half of the Middle Cambrian 

 and the order Hymenocarina continues on up into the Ordovician, 

 Silurian, and Devonian. 



^ Bull. Geol. Soc. America, Vol. 10, 1899, p. 238. 

 ^Smithsonian Misc. Coll., Vol. S7, No. 3, 191 1, p. 28. 

 ^ Idem, p. 27. 



* Sixteenth Ann. Kept. New York State Museum, 1863, pp. 181 and 182, pi. 

 II, figs. 7-16. 



° American Journ. Sci., Vol. 12, 1901, pp. 364-366, pi. 7. 



* Tenth Ann. Kept. U. S. Geol. Survey, 1891, pp. 625 and 626, pi. 80, figs. 

 ID and loa. 



