NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 5 



graphic and structural evidence had previously reached the conclusion 

 that by and large the strata on the Griswold farm become progres- 

 sively younger toward the east, which would confirm the suggested 

 order. He also considers all these strata higher than the Ashley Hill 

 Conglomerate. Since the latter holds the Elliptocephala fauna not 

 only in boulders, but also in a regularly bedded limestone interval 

 at the base of the conglomerate, one might conclude that the latter 

 fauna is older than the Acimetopus and Pagetides faunules. 



The Elliptocephala asaphoides assemblage extends through a con- 

 siderable thickness of strata in Washington County (Lochman, 1956; 

 Theokritoff, 1964), It is possible that the difference between the 

 Acimetopus bilobatus faunule and that assemblage is one of environ- 

 ment rather than age. A faunule reported by Theokritoff (1964) 

 from Washington County, believed to be somewhat younger than the 

 typical Elliptocephala asaphoides assemblage, shows no particular 

 resemblance to the one described herein. 



The Acimetopus bilobatus faunule is notable for the number and 

 variety of trilobites of the family Eodiscidae, of which 9 new genera, 

 20 new named species, and an unnamed one are described herein, 

 all based on cephala. A few unassigned pygidia, in part possibly 

 representing additional species, are also described. None of the 

 Eodiscidae can be referred to previously known species, even though 

 several are referable to the well-known genera Calodiscus and Ser- 

 rodiscus. 



The Olenellidae are represented by numerous fragments of small 

 individuals, referable to three species, none of which is the common 

 Elliptocephala asaphoides known from numerous localities in the 

 Taconic sequence of Washington, Rensselaer, and Columbia Coun- 

 ties. Immature Olenellid cephala cannot be specifically identified by 

 comparison with adult individuals, and even the generic reference 

 may remain doubtful, since several of the genera were based on the 

 features of the entire exoskeleton. Two of the species are tentatively 

 referred to Paedeumias and one to Olenellus; none shows close 

 resemblance to named species. 



The opisthoparian trilobites are represented by four undetermined 

 species of Bonnia, a pygidium referred to Kootenia, and a peculiar 

 pygidium belonging to an undescribed genus of uncertain affinities. 



Conspicuously absent from the Acimetopus bilobatus faunule are 

 Eodiscids with eyes and facial sutures, which constitute the family 

 Pagetiidae, even though species of Pagetides are the most common 

 trilobites in the nearest fossiliferous outcrop. Also totally absent are 



