244 PALEONTOLOGY 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. 

 QLhlert* 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 



* Fisohbr's Manuel de Conchy liologie, p. 1311. 



