6 
PALEONTOLOGY OF NEW YORK. 
angles, which develop from the sides of the delthyrium and meeting, enclose 
wholly or partially a circular or oval pedicle foramen. At normal maturity 
these plates become anchylosed along the median suture and form a single con¬ 
vex plate (the so-called pseudodeltidium). 
The usual absence of the deltidium may be due either to accidental removal 
or to resorption with advancing growth. In the adult and senile stages of de¬ 
velopment many species, especially in the line of development to Syringothyris, 
form a testaceous callosity in the pedicle-cavity, thickening the umbo and ex¬ 
tending across the delthyrium, reaching in extreme cases, nearly to the cardinal 
margin. 
The muscular area consists of a subtriangular pedicle-impression occupying 
the pedicle-cavity, and continuous with a deeply impressed oval or obcordate 
area, which is posteriorly situated and divisible into a narrow median adductor 
and broad lateral diductors, the surface of the latter being marked by radiating 
or racemose furrows. The posterior and anterior members of the diductors 
may frequently be distinguished, the former being of less extent and their sur¬ 
face markings somewhat different from those of the latter. 
A median septum in this valve is usually absent; occasionally it is in a con¬ 
dition of incipient development, and in certain species having the aspect of 
Spiriferina and belonging to the line of descent of which this genus may be 
regarded as the final or accessory product, it forms a most conspicuous feature 
of the interior. 
In the brachial valve the umbo is inconspicuous, the apex only being in¬ 
curved over the cardinal area; a median fold corresponds to the sinus of the 
opposite valve. The cardinal area is narrow and divided by a broadly triangu¬ 
lar delthyrium. The dental sockets are narrow, moderately deep and bounded 
interiorly by highly developed socket walls, the extremities of which support 
the crural bases. 
The cardinal process is a low, transverse, sessile apophysis, having its surface 
vertically striated; occasionally it is bipartite or it may be wholly resorbed. 
The crura are long, straight and slightly divergent; their union with the 
primary lamellae of the spiral ribbon is at a broadly obtuse angle. The brachial 
