[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 171 



mon, and one species appears that is not present in the older sub-zones 

 in the St. John group. The species that are continued from the lower 

 sub-zones are mostl}'' imitations of the earlier forms. Of the several 

 sections of the Agnosti occurring in this sub-fauna, the Parvifrontes are 

 the most numerous in individuals. The species A. umbo is the most com- 

 mon, and seems to be the highest expression of variation into which the 

 Parvifrontes run. The Lievigati appear in the Acadian Cambrian 

 Faunas here for the first time, and the impression of the glabellar margin 

 on the inside of the test shows that they originated from the same stock 

 as Agnostus umbo. 



Thus this sub-fauna, like that of the Andrarum Umestone at the 

 summit (almost) of the Paradoxides beds in Sweden, exhibits the ex- 

 treme variation of the Agnostoid stock, though ours, as yet, not in the 

 same rich varietv as that of the Old World. 



Agnostus nathorsti, Brugg. ? mut. (PI. I., tig. 2). 



A'jnostiis Nathorsti, W. C Brogger, Paradoxides skifrene ved Krek- 

 ng, i Nyt. Mag. f. ^aturvid. 24 Binds 1 Hefte, p. 68, tab. v., tig. 1. 



Agnostus Nathorsti, S. A. Tullberg, Agnostus arterna v. Andrarum. 



Agnostus Nathorsti Faunas of Paradoxides beds Trans. IST. Y. Acad. 

 Sci., vol XV., p. 29, tig. 9, pi. 1(>, tig. '^a and h. 



A pygidium which will probably be found to belong to this species, 

 though ditfering from that which occurs with the P. Abenacus sub- 

 fauna in the St. John Basin, is present in the dark .siliceous shales. 



This pygidium is less elongate than the form figured b}^ Tullberg 

 and Brogger as occurring at Andrarum. and the marginal spines are 

 placed further back. The rachis is shorter and less acuminate, and the 

 anterior lobe is wider and larger. It is less quadrate than the form in 

 Div. \d. i. ("Abenacus sub-fauna) of the St. John Ciroup, and the lateral 

 spines are less prominent, and further back on the margin ; otherwise 

 it aijrees better with this than with the Scandinavian form. 



Agnostus fissus. Lundgren. 



Ayuo>ifusfissus, Lundi;;. Liiinarsson, Oin faunan i Kalkeii med Conoc. exsulens 

 p. 2:3, taf. ii., fig. 34. 



Agnostus fissus, Tullberg, Agnostus arterna v. Andrarum. p. 16, pi. i., fig. 3. 



Agnostus fissus, Faunas of the Paradoxides Beds in E. North America. Trans. 

 N. Y. Acad. Sci., p. 230, pi, xvi., fig. 10. 



A single head-shield, poorl}' preserved, has the characteristic furrow 

 on the anterior lobe of the glabella, and the long tubercle on the front of 

 the posterior lobe. It is from the dark siliceous shales. 



