SYRINGOTHYRIS 385 



split longitudinally internally, this split tube, together with the extension 

 of the delthyrial plate, being termed the syrinx. In some cases the 

 syrinx is solid. A pseudodeltidial covering of the delthyrium entirely 

 separate from the delthyrial plate and syrinx is sometimes present. The 

 muscular scars as in Spirifer. The brachial valve essentially as in 

 Spirifer, both externally and internally. Shell structure punctate 

 throughout except in the central, vertically striated region of the car- 

 dinal area. The external surface covered with a minute, textile-like 

 ornamentation except upon the central region of the cardinal area. 



Remarks. The genus Syringothyris represents a specialization of the 

 Spirifer type which is characterized by the development of the syrinx, the 

 punctate shell structure, the high cardinal area and the peculiar character 

 of the minute surface ornamentation. Except the shell structure and 

 the minute ornamentation of the shell, which frequently can not be 

 recognized because of the condition of preservation, the distinguishing 

 characters are confined to the pedicle valve, indeed, from the brachial 

 valves alone not even the species can be successfully identified. The 

 brachial valves differ from any of the corresponding valves of the Mississ- 

 ippian Spirifers, however, with which they might be confused, by reason 

 of the absence of plications upon the fold and sinus. 



Much has been written of the genus and its characters have come to 

 be firmly established. Much confusion still exists, however, among the 

 species composing the genus, and in almost no case have the essential 

 specific characters even been accurately pointed out. Schuchert 1 re- 

 ferred most of the Mississippi basin forms to these three species, 8. 

 carteri, 8. extenuatus, and 8. textus, considering no less than five other 

 forms as synonyms under these three, but a careful investigation of a 

 large amount of excellent material in which nearly every described form 

 is well represented, besides some undescribed ones, has led the writer to 

 the conclusion that most, if not all, the named species are good, although 

 their really essential characters have not been clearly pointed out. In 

 characterizing the species of the genus the brachial valves are of almost 

 no value whatever, and when that valve alone is preserved for study, 

 it is in most cases impossible to identify it. The essential specific char- 

 acters are found in the pedicle valve and consist in the proportional height 

 of the cardinal area, its degree of curvature, whether flat, concave, or con- 

 vex, and especially in the size of the angle between the flatter portion of 

 the area and the plane of the valve, this angle varying among different 

 species from 25 to 110 degrees or more, but being fairly constant among 

 different individuals of the same species. Another set of characters which 

 seem to be of prime importance in specific differentiation are the char- 



i 9th Ann. Rep. N. Y. State Geol., pp. 28-37. (1890.) 

 13 



