244 
PALjEONTOLOGY of new YORK. 
dylium in the brachial valve supported by a single axial septum. Pentamerus 
fornicatus is a small shell with a few broad, obscure plications, the most con¬ 
spicuous lying in the sinus of the pedicle-valve. The whole expression of its 
exterior is very similar to P. Barrandii, Billings, from the Anticosti series, 
though the latter is an elongate and much larger shell, interesting in having 
the sinus and fold, in immature growth-stages, on pedicle- and brachial valves 
respectively, but reversing this arrangement at maturity. This reversion is, 
however, to some extent illusory and need not affect the association of the 
species with P. fornicatus; it is essentially due to the plication in the sinus of 
the immature pedicle-valve, which, after middle growth, fills up, and entirely 
obliterates the sinus itself; the effect in the mature shell being intensified by 
the corresponding development of the axial furrow on the immature fold of the 
opposite valve. 
A peculiar internal character of all these shells is the series of strong 
vascular, or ovarian sinuses, which radiate from the umbonal region of the 
pedicle-valve. These are complicated with the undefined diductor scars and 
are therefore to a certain extent of muscular origin. In Pentamerus fornicatus 
these are highly developed and produce strong ridges on the casts of the valve; 
while in P. ventricosus they are more numerous and much finer. In P. linguifer 
the character of the inner surface of the valves has not been described, but in 
transverse sections we find evidence that these sinuses were highly developed. 
It was for similarly ridged internal casts that Barrande proposed the generic 
term Clorinda {C. armata, Etage G, type ; C. ancillans, Etage E), both his 
species being pentameroids which in external form were probably not unlike 
P. linguifer. 
No name has been introduced which can be appropriately employed as a 
designation for this group of species typified by Pentamerus linguifer, Sowerby. 
Q^hlert^ has given to the term Antirhynchonella, Quenstedt, 1871, a value 
which would justify its use in this case were it not that the French author has 
evidently misinterpreted the original application of this name, which was inci¬ 
dentally suggested for such pentameroids as have the position of the median 
* Fischbk’s Manuel de Conchyliologie, p. 1311. 
