GASTROPODA. 869 
Protowarthia rectangularis. ] 
entire shell; sinus deep, the lobes not rounded but bending at almost a right angle 
in the middle; inner lip slightly reflexed and thickened on each side; test thin, 
composed apparently of two layers, the inner nacrous. Surface of specimens marked 
by more or less obscure lines of growth. These are usually the strongest on the dor- 
sum, where they may be seen also on some casts of the interior. The latter, however, 
are in most cases quite smooth and without a trace of markings. External 
layer of shell not seen in good condition, so we cannot say positively, though 
we suspect it to be so, that it was marked near the umbilicus, as in the following 
species, by fine granulose striz. Hight of shell 20.5 mm.; median hight of aperture 
8.3 mm.; width of same 19 mm.; width of inner volution 7 mm.; depth of sinus 8 mm. 
In two other specimens, one very large, these dimensions are respectively, 24, 10, 23, 
7 and 9 mm., and 30; 13.5, 27, 8 and 12 mm. 
This species is often met with in collections under the name of Bellerophon 
bilobatus, but it is really quite distinct, as anyone may see by comparing the 
accompanying figures of that species with those of B. rectangularis given on plate 
LXIII. 
A B C 
Fig. 3. A and B, two views of Protowarthia bilobata Sowerby sp., and ©, two views of Bellerophon 
(?Oxydiscus) acutus Sowerby; Caradoc sandstone, England. Copies of the original figures of these species on 
plate x1x of Murchison’s ‘Silurian System,” 1839. - 
It will be noticed that B, bilobatus, or Protowarthia bilobata as it should now be 
called, is a more ventricose shell, causing the back to be fuller and much more 
broadly rounded, while the apertural lobes, are, as usual, rounded in front instead 
of angular. The rectangular outline of the apertural lobes which has suggested the 
specific name, distinguishes P. rectangularis from all the other forms referred to 
Protowarthia. Indeed, it is a peculiarity that is not possessed by any other species 
of the whole suborder. 
We have before us three specimens of a variety of this species from the Trenton 
limestone at Trenton Falls, New York. So far as this material at hand shows, the 
variety differs only in having the apertural lobes less angular than usual. We have 
also a number of internal casts from the Black River and Trenton shales and 
