324 MISSISSIPPIAN BRACHIOPODA 



upon the lateral slopes of the shell ; lateral slopes of the valve depressed 

 convex, marked by plications similar in form and number to those of the 

 opposite valve. 



The finer surface markings of the shell have only been observed upon 

 squeezes taken from natural moulds which do not perfectly preserve their 

 character. They consist, so far as can be seen, of fine, concentric, sub- 

 lamellose lines of growth which are more or less crowded at intervals, 

 especially towards the front of the shell. 



Remarks. This species has only been observed in the condition of de- 

 tached and more or less incomplete separate valves, and in this condition 

 it is not always easy to distinguish between it and S. platynotiis, with which 

 it is sometimes associated. It does not attain so large a size as 

 S. platynotus, it does not exhibit so great variation in the lateral extension 

 of the hinge-line, being uniformly more extended than that species and 

 with the angular cardinal extremities more acuminate, the lateral bound- 

 ing plications of the sinus of the pedicle valve are conspicuously broader 

 and more differentiated from the other plications of the valve, the sinus 

 itself is narrow and has but one lateral plication on each side which is 

 less sharply differentiated from the bounding plication than from the 

 median one. The fold of the brachial valve in the two species is similar 

 in being little or not at all elevated above the general surface, but it is 

 more sharply differentiated in 8. biplicoides. 



The species differs from 8. lonisianensis in its proportionately broader 

 shell, more extended cardinal extremities, shallower pedicle valve with 

 broader umbonal region and lower cardinal area. The bounding plications 

 of the mesial sinus of the pedicle valve are also broader and more differ- 

 entiated in this species than in 8. louisianensis. 



Members of this species were originally included by Hall under his 

 species 8. biplicatns, indeed, of the two specimens figured as the types of 

 that species, one is an example of S. biplicoides. The distinctions between 

 the two species are pointed out under the discussion of 8. biplicatus, but 

 besides being different in character, the two forms occur at different 

 geologic horizons within the Kinderhook. 



Horizon. Kinderhook. 



SPIRIFER INSCULPTUS Rowley 

 Plate XL, Figs. 30-34 ; Plate XLI, Figs. 1-5 



1900. Spirifer insculptus Rowley, Am. Geol., vol. 25, p. 268, pi. 5, figs. 

 1-3. 



Description. Shell above medium size, much wider than long, the great- 

 est width along the hinge-line, the cardinal extremities acutely angular. 

 The dimensions of a nearly perfect specimen, the holotype, are : length of 

 pedicle valve 24 mm., length of brachial valve 20 mm., width along hinge- 



