C. Schuchert — Brachiojpod genus Syringothyris. 223 



Art. XXIII. — On the Brachiojood gentis Syringothyris in the 

 Devo7iian of Missouri ; by Charles Schuohert. 



(Contributions from Peabody Museum, Yale University, New Haven, Conn.) 



American species of Syringothyris are said to be restricted 

 to the Lower Carboniferous or, better, the Mississippian, and 

 are known to ran^e from the base of this system into tlie Sper- 

 gen formation (Lanesville, Indiana). Professor Greger, of 

 Fulton, Missouri, recently sent the writer specimens of Cyrtia 

 occidentalis Swallow (Trans. St. Louis Acad., i, 1860 : 648) 

 that are unmistakable individuals of Syringothyris. These he 

 gathered from the type locality of the species in the Callaway 

 limestone at Bellamy Springs and elsewhere in Callaway 

 County, Missouri. This limestone is here the basal member 

 of the Devonian invasion, and appears to be either of late 

 Middle or early Upper Devonian time. 



The syrinx in S. occidentalis is as well developed as in S. 

 hannihcdensis, in both of which this plate, for pedicle muscle 

 attachment, has not yet developed into the typical form de- 

 scribed as the split tube by Hall and Clarke (Pal. N. Y., viii, pt. 

 ii, 189i : 48). In these species the under side of the syrinx is 

 slightly concave, widely open along the inner free end, and is 

 marked by converging muscular gi'owth ridges medially di- 

 vided by a faint septum. In S. hannihalensis the lateral walls 

 of the syrinx close inward and form a more or less well-devel- 

 oped split tube. In other and later species the tube is solid 

 and only the innermost free end has a short depression to 

 which the pedicle muscles are attached. 



S. occidentalis is as a rule less transverse than the other spe- 

 cies of Syringothyris, and in this is most like the earliest Missis- 

 sippian species. In the later forms S. carteri and S. texta 

 the valves are more transverse. 



Keyes was the first to refer Swallow's species to Syringothyris 

 (Missouri Geol. Surv., v, 1894 : 86), but as he gave no reasons 

 for this reference and as the writer (Bull. IT. S. Geol. Surv., 

 87, 1897 : 199) had not then seen this shell, he preferred to 

 follow Miller's North American Geology and Paleontology, 

 where it is placed doubtfully iinder Cyrtina. 



Syringothyris therefore originated in the Cordilleran sea 

 during the later Devonian and not in the Atlantic province 

 as the writer heretofore held, but it was not a conspicuous 

 member of any fauna until Mississippian time. The genus is 

 then present in most of the formations from the early Kinder- 

 hook to the Keokuk, and it persists even into the Spergen of 

 the Meramecian series. At uo time, however, w-as tliere more 

 than one species in a fauna and all these are very much alike. 



