718 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
strong, and the vascula media take their origin at the anterior end of the diductor 
muscle on the callosity. Another pallial trunk of importance originates at the 
anteromedian edge of the ovarian impression. The latter are small and seem to 
be better developed in the pedicle than the brachial valve. 
The cardinal process is of interest because it seems to have no shaft or at least 
a minimum development of that structure. The process arises abruptly from the 
notothyrial platform and extends toward the pedicle valve. Its anterior face is 
somewhat excavated but the myophore bears 3 prominent septa. The cardinal 
process is reinforced by shell material deposited on the inside of the brachio- 
phores, giving the appearance of the latter structures being welded to the cardi- 
nal process. It does not, however, present the tentlike, deeply excavated plate 
of Sowerbyella. The brachiophores are short and inconspicuous rods. The 
median ridge is low in the adductor field but is elevated at its anterior end and 
must have partitioned the anterior of the shell cavity into two chambers. As in 
the pedicle valve the brachial valve has a thickening of shell material laid more 
or less parallel to the posterior margin and just anterior to it. This taken in 
conjunction with the ridge of the pedicle valve may have helped in shell 
articulation. 
Titanambonites is most like Sowerbyites of American genera. The pedicle 
valves of the two genera are very close, but the brachial valves are quite different. 
In Titanambonites no lateral septa have yet been observed, and the form of the 
median ridge is different. Of European genera Leptestia is most like Titanambo- 
nites. In the case of Leptestia differences occur inside both valves. Leptestia 
has a small delthyrial cavity to which the muscle scars are confined. This cavity 
is bounded by ridges suggestive of dental plates but possibly of different origin. 
Anterior to the muscle field is a low median ridge which separates two excep- 
tionally large subreniform ovarian impressions. The brachial valve of Leptestia, 
too, is characterized by an exceptionally large subreniform ovarian impression 
occupying most of the shell surface. The median septum of Leptestia is more 
elevated than that of Titanambonites, and the cardinal process has a pronounced 
shaft. The myophore, chilidium, and adductor field are like those of the American 
genus. 
TITANAMBONITES AMPLUS (Raymond) 
Plate 177, A, figures 1-10; plate 179, A, figures 1-6; plate 180, B, figures 14-16; 
plate 194, B, figures 11-18; plate 206, C, figure 13 
Plectambonites amplus RAyMonp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, 
p. 207, pl. 2, fig. 9; pl. 3, fig. 12, 1928. 
Large for the genus, wider than long and with the hinge forming the widest 
part ; sides sloping slightly obliquely toward the middle; anterior margin broadly 
rounded. Costellae low, thin, rounded, and distant, about 2 or 3 to the millimeter ; 
concentric fila strong. 
Pedicle valve strongly convex in lateral profile, fairly strongly domed in an- 
terior profile; beak scarcely protruding posterior to the posterior margin; umbo 
moderately swollen, marked by a narrow, short fold at the beak; median region 
