PSEUDOSYRINX 405 



the lateral slopes of the valve, than in Syringothyris. The little shell which 

 has been described as Syringothyris missouri H. & C. has the external as- 

 pects of Pseudosyrinx, the long dental lamellre and the rounded lateral 

 margins of the cardinal area, and were it not for the fact that the syrinx 

 has actually been observed in the type specimen, the species would be 

 placed in this new genus. P. missouriensis, described in this report as a 

 new species, is designated as the genotype of the new genus. 



Pseudosyrinx differs from the genus recently described by Kindle as 

 Syringospira, 1 in the continued divergence of the dental lamellae through- 

 out their entire length, and in the absence of plications upon the fold and 

 sinus. In Kindle 's genus the dental lamellae converge anteriorly so as to 

 become united a short distance in front of the apex of the valve and form 

 with the delthyrial plate a subconical or tube-like chamber in the poste- 

 rior portion of the pedicle valve, with its opening directed towards the 

 opposite valve. 



PSEUDOSYRINX SAMPSONI Weller 

 Plate LXVII, Figs. 11-13 



1909. Syringothyris sampsoni Weller, 'Bull. Geol. Soc. Am., vol. 20, p. 

 311, pi. 14, fig. 4. 



Description. Shell large, wider than long, the greatest width at or near 

 the hinge-line, the cardinal extremities apparently a little rounded or per- 

 haps subangular. The dimensions of the holotype, a somewhat crushed 

 specimen, are : length of pedicle valve from beak to front, approximately 

 50 mm., length of brachial valve approximately 45 mm., greatest width 

 approximately 77 mm., length of hinge-line approximately 74 mm., height 

 of cardinal area 56 mm., width of delthyrium at base 16 mm., width of 

 sinus in front approximately 28 mm. 



Pedicle valve subpyramidal in form, the surface sloping steeply from 

 the umbonal region to the lateral and anterior margins ; mesial sinus non- 

 plicate, of moderate depth, rounded in the bottom, not sharply defined 

 laterally, produced in front in a rounded lingual extension ; beak small, 

 pointed, slightly incurved; cardinal area of great height, nearly flat ex- 

 cept just under the beak where it is a little concave; it slopes anteriorly 

 from the hinge-line to the beak in the type specimen at an angle of appar- 

 ently 30 degrees, although this may be too small ; the lateral margins are 

 not well preserved in the type but they apparently round rather abruptly 

 into the lateral slopes of the valve, the triangular, vertically marked dif- 

 ferentiated region lying on each side of the delthyrium has a width of 

 base along the hinge-line about twice that of the base of the delthyrium 

 and less than one-half the total length of the hinge-line ; the delthyrium 

 is narrowly triangular, its height being about three times its width at 



1 Bull. U. S. Geol. Survey, No. 391, p. 28. (1909.) 



