798 CAMBKIAN BRACHIOPODA. 



Genus SYNTBOPHIA HaU and Clarke, a 



Syntrophia Hall and Clabke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, footnote, p. 270. (Discusses 



species which appear to belong to a distinct genus and announces the future use of the term Syntrophia to 



include them.) 

 Syntrophia Hall and Clarke, 1893, idem, pt. 2, pp. 216-218. (Described and discussed as a new genus, copying 



the original note proposing the genus. The description of ' ' Triplesia lateralis " Whitfield, which is given on 



p. 217, is copied in this monograph; see below.) 

 Syntrophia Hall and Clarke, Hall, 1894, Thirteenth Ann. Rept. State Geologist New York for 1893, vol. 2, pp. 836- 



837. (Copies the description of "Triplesia lateralis " given on p. 217 of the preceding reference.) 

 Syntrophia Hall and Clarke, Walcott (in part), 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 288-289. (Gives an essential 



copy of the description of "Triplesia lateralis" given by Hall and Clarke, 1893b, p. 217, a description which 



is copied below, and discusses the genus essentially as below. Species were included in the genus which are 



now placed under Euenella.) 

 Syntrophia Hall and Clarke, Grabau and Shimer, 1907, North American Index Fossils, vol. 1, p. 270. (Described.) 

 Syntrophia Hall and Clarke, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 148. 



(Classification of genus.) 



The description of "Triplesia lateralis" by Hall and Clarke [1893b, p. 217] follows: 



Shell transversely elongate, biconvex with a straight hinge line whose length nearly equals the greatest diameter 

 of the valves, and each valve is medially divided by an open delthyrium. The external surface is smooth, with fine 

 concentric lines \dsible only about the margins; the inner shell layers show a strongly fibrous radiating structure 

 without punctation. The pedicle valve bears a more or less clearly developed median sinus and the brachial valve 

 a broad, indistinct fold. 



On the interior the teeth are very small, lying at the extremities of the delthyrial margins and supported by 

 dental plates which converge and unite before reaching the bottom of the valve. Thus is formed a deep but short 

 spondylium, which is supported, near its apical portion, by a median septum, but is free for fully one-half its length. 



In the brachial valve there are also two convergent plates bounding the deltidial cavity, larger and stronger than 

 those of the opposite valve. These plates may rest upon the bottom of the valve, and probably always do so toward 

 the posterior extremity, but anteriorly they become free, forming a spondylium which is supported by a median septum 

 extending beyond the anterior edge of the plate. Thus these two valves which are very similar in exterior, the pedicle 

 valve being only slightly the more convex and with a low median sinus, are also closely alike on the interior, each 

 being furnished with a spondylium. 



Type. — Triplesia lateralis Whitfield. 



Observations. — Hall and Clarke [1893b, p. 216] referred Ortliis harahuensis and Triplesia 

 primordialis among Cambrian species to Sijntrophia, and of Ordovician species, Triplesia 

 lateralis, StricMandinia? aretliusa, S.f aracJine, and Camarella calcifera. 



Orthisf armada Billings, of the Lower Ordovician, certainly has a close resemblance in the 

 spondylium of its ventral valve to this genus, and it may represent a radially striated form, as 

 suggested by Hall and Clarke [1893b, p. 218]. Concerning the relations of Syntrophia to Strick- 

 landinia, they consider that the structures represented in the species referred to the former 

 genus may be the equivalents of those represented by the Stricklandinias of the later Silurian 

 and Devonian. Billings [1862b, p. 84] noted the relationship existing between his Camarella 

 calcifera and StricMandinia. It is probable that S. f arachne, S. aretliusa, and similar forms 

 should be referred to a distinct genus. They are not typical Stricklandinias and they differ 

 in surface and shape from Syntrophia lateralis. 



The Cambrian type of Syntrophia is S. rotundata of the Upper Cambrian. It has a spondyl- 

 ium in each valve supported by a median septum, and a short area divided by a large open 

 delthyrium. 



The structure of the shell of Syntrophia is fibrous, with rows of minute pores between 

 the fibers. 



a The synonymy for this genus does not give a complete record of the various genera under which the species now included in Syntropliia were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record tor the species taken up in 

 this monograph the following mere generic references are listed; s 



Camerella Billings [1861a, p. 318; 1863, p. 231]. 



Orlhis A. Winchell [1864, p. 228]. 



Camerella Billings [1865a, p. 220]. 



Triplesia Whitfield [1878, p. 51]. 



iepteM Whitfleld[1878, p. 60; 1882, pp. 171 and 195). 



Triplesia Whitfield [1882, p. 172]. 

 Triplesia Walcott [1884b, p. 75]. 

 Triplesia Whitfield [1886, p. 303]. 

 Triplecia Hall and Clarke 11892c, p. 270). 



