104 THE DEVONIAN OF MISSOURI. 



Syringothyris n. sp. 

 Plate 20, figures 1 and 2 



One specimen of Syringothyris has been collected from the Mineola. It is an 

 internal mould and imperfectly preserved. The following notes on the specimen are 

 from a letter of Prof. J. E. Hyde: 



"Specimen is an interior mould of a new species of Syringothyris, properly a Pseudo- 

 syrinx if that genus proves of permanent value. It is a pedicle valve with high, flat 

 cardinal area standing at between 80 degrees and 87 degrees to the plane of the valve. 



L. Br. 



Length of pedicle valve, 22.7 mm., brachial valve about 14.5 mm. Ratio .64. 



L. Pd. 

 Height of cardinal area 17.3 mm., breadth of cardinal area, 23 mm. Greatest breadth 

 of pedicle valve 28 to 29 mm. Width of delthyrial opening at hinge about 8 mm. From 

 this it would be seen that the hinge line is narrower than the greatest width of the valve. 

 Greatest width of valve about half way between cardinal area and anterior margin. 

 Width of sinus at anterior margin 13 mm., or nearly half the greatest width of the valve. 

 Sinus broadly concave, its margins rather abruptly bent into the strongly convex sides 

 of the valve which are rounded to meet the cardinal area at an obtuse angle. Dental 

 lamellae, where attached to the cardinal area but moderately divergent to form a high, 

 narrow delthyrial opening, the whole essentially flat, and parallel to the plane of the 

 cardinal area or but slightly pointing into the valve, but slightly sunken below the 

 plane of area. The free end is a flat, or very slightly concave, triangular point, one-third 

 the total length of plate, with no upturned edges, exactly the stage of the syrnix made 

 by Weller characteristic of his genus Pseudosyrinx. As in many other species examined, 

 the triangular tip shows what appears to be a clearly defined muscle scar. This Pseudo- 

 syrinx or flat-plate stage is commonly found in the older species of Syringothyris, is 

 clearly primitive, and this mid-Devonian species runs true to form in its possession. 



Some years ago I examined a suite of authentic Syringothyria occidentalis Swallow 

 from the Callaway limestone of Missouri. This Devonian form, as I now recall it, is 

 wholly distinct from the one you present. That species is possessed of a high, flat 

 area bending by sharp angles into the flattened sides of the valve, and these in turn 

 rather abruptly into the shallow, broad sinus; there is very little curvature along any 

 line from the beak to the free margin, and the result is a high, pointed, rigid, sub- 

 pyramidal aspect that is characteristic. 



Syringothyris chemungensis Cushing, from the Ohio Chagrin, which is Upper 

 Devonian, has its greatest width at the hinge and acute or 90-degree cardinal angles, 

 transverse plate much larger, occupying half the length of the delthyrial opening or more, 

 syrinx on whole a little more advanced in type, with recurved edges suggesting begin- 

 ning of a tube, though occasional individuals show same stage as yours. , 



Your specimen with its delicate transverse plate, sunken but slightly below the 

 cardinal area, has almost nothing in common with those early Syringothyri from Warren, 

 Pa., described by Simpson as S. randalli and angulata, with their narrow arched areas 

 and thick, massive, spine-like, highly-inclined, transverse plate, sunken far below the 

 plane of the area." 



Remarks — Schuchert's 1 earlier supposition that Syringothyris originated in the At- 

 lantic province rather than the Cordilleran is supported by the presence of this speci- 

 men in the Mineola. However, the two provinces were not as distinct as was supposed. 



'Am. Jour. Sci. XXX, p. 223. 



