376 Dr. Hunt on the Primordial Zone 



pygarum^ tliat is to say in the alum slates with limestone beds, 

 which contain the first portions of the second fauna in Sweden. 

 In accordance with this fact, it would appear that the cephalopoda 

 indicated by Mr. Billings in his 2nd group must be referred to 

 the second fauna. 



"The gasteropods furnish to the second group six genera, 

 which are commonly found in the second fauna of various coun- 

 tries, but as these types are reproduced in the third fauna, their 

 presence here has no bearing upon the question before us. 



"The acephala are only represented by the new genus Cyr- 

 todonta lately established by Mr. Billings, according to whom the 

 eleven species of this genus already described, belong to the Black 

 River and Trenton limestones, i. e., to the second fauna of Canada, 

 although allied forms may also occur in the third fauna. (^Canadian 

 Naturalist, December 1858, p. 331.) 



" The class of brachiopods, which is relatively but little de- 

 veloped, otfers four genera, Lingula, Orthis, Strophomena and 

 Camarella, which last genus was founded by Mr. Billings in 

 1859, to include several species of the second fauna of Canada, 

 {^Canadian Naturalist^ August, 1859, p. 301). Nothing however 

 indicates that similar forms may not also occur in the third fauna, 

 as is the case with the three other genera mentioned. Thus the 

 fossils of this class, generically considered, establish nothing as to 

 the geological horizon of the second group, although it is very 

 probable that the study of their specific forms may aid us in 

 finding its horizon. 



" The bryozoa furnish to the second group a form of Dic- 

 tyonema ; a type which although signalized in the Primordial 

 Zone of diff'erent countries, does not appear to be confined to that 

 horizon. The specific nature of the form in question has not yet 

 been determined. 



" In conclusion we may say that the association of Ag- 

 nostus with the various other genera which we have just 

 passed in review, seems to shew in a positive manner that the 

 second group belongs to the second fauna. This conclusion may 

 be extended with still greater reason to the group No. 3, which 

 contains only the genus Asaphus, represented by two species. 

 This type has never been signalized either above or below the 

 second fauna, of which it constitutes one of the most marked and 

 most constant characters. The second and third groups con- 

 sidered palseontologically, then represent simply phases of the 

 second fauna. 



