PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 133 
bers of this genus available for study have been examined with great care, but 
no basis was found for generic separation anywhere along the line. 
The Craniidae appear in this part of the Ordovician well formed except for 
two possible genera and proved to be fairly common in places. The cemented 
habit seems to have been well established. Eoconulus is a small cone that is 
abundant in the suite of formations at the base of the rocks deposited in the 
Porterfield stage. Only brachial valves that have a primitive musculature are 
known. These are not postulated as the forerunners of the Craniacea because 
Acanthocrania, a more standard genus, occurs with them. 
A form of uncertain relationships, Undiferina, possibly was a cementing 
brachiopod. The median septum and general form of the one known valve sug- 
gest relationship to Conotreta and allies rather than to the Craniacea. It is pos- 
sible that the Acrotretacea may have developed a cemented form, but this is not 
yet positively known. 
The insoluble residues from the Pratt Ferry limestone yielded a number of 
forms of which single valves only are known. Perhaps the most peculiar among 
these is the brachiopod here called Trematis ? spinosa, which at present is known 
only from the brachial valve. This valve contains a tuft of spines on the hinge 
area. The purpose of these spines cannot at present even be conjectured. Spines 
such as these on the opposite valve might have been used for attachment in early 
stages as they are in the Productacea, but attachment spines on a brachial valve 
are at present unknown. The Pratt Ferry residues have opened the door only 
a slight crack but have permitted a fleeting glance at the form and habits of a 
wonderful world of inarticulate brachiopods. Much of significance and interest 
to morphology and classification is yet to come from these shells that have been 
thought to be retarded in evolution and diversification. 
Pygocaulia.—This monograph contains many new articulate genera that have 
been revealed by extensive collecting and also by the acid treatment of limestones. 
The Pratt Ferry limestone has produced some of the most unusual forms. The 
Effna-Rich Valley limestone, Botetourt formation, and Arline formation, all be- 
longing to a related suite of beds which are likewise related to the Pratt Ferry 
formation, have yielded other odd genera. The result is that some families have 
become unexpectedly large and much has been learned about hitherto poorly 
known brachiopods. 
The Table Head series and upper Pogonip group have yielded their share of 
unclassifiable material. These formations form a sort of bridge between the 
Lower Ordovician (Canadian) rocks and those laid down in the Marmor stage. 
They have produced brachiopods that are intermediate in their structure between 
the Canadian ones and the higher genera. An example is Syndielasma which 
is prophetic of Sowerbyella but differs in not having the cardinalia welded to- 
gether as in the later genera. Hesperomena is a more primitive leptellinoid than 
the higher ones as it does not have the visceral disk elevated. The Table Head 
brachiopod fauna gives indications of containing numerous genera that will plug 
gaps in the developmental stages of the families of the Middle Ordovician brachi- 
opods when it is fully studied. 
