288 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



«pecimens .showing- tine casts of the area, delth3'riuni, and unibonal 

 cavity. 



Ohi^ervatloiis. — This tine species is unique amonj*; Cambrian brachi- 

 opods in having a depressed, flat, or convex ventral valve and strongly 

 convex dorsal valve. In its^ punctate shell, free spondyliuni, and 

 absence of cardinal process, it is allied closely to Protorthis; the 

 depressed ventral valve and convex dorsal valve serve to distinguish 

 it as a subgenus of Protorthi^^ which 1 have called Lcyperia in recog- 

 nition of the effective work of Mr. S. Ward Loper, who collected 

 the material representing this and many other Cambrian fossils in 

 Cape Breton and New Brunswick. 



Foriiiation and locality. — Middle Cambrian. Division 2 — probably 

 2b — of Matthew's section. Dougald Brook, tributary to Indian River; 

 one-fourth mile from lower bridge, P^scasonia, Cape Breton, Nova 

 Scotia. 



SYNTROPHIA Hall and Clarke. 



Syntrophia Hall and Clarke, Pal. N. Y., VIII, 1892, Pt. 1, p. 270; 1893, Pt. 2, 

 p. 216; Thirteenth Ann. Rep. State Geol. N. Y., 1895, p. 836. 



Original description. — Shell transversely elongate, biconvex, with straight hinge- 

 line, whose length nearly equals the greatest diameter of the valves; each valve 

 medially divided by an open delthyrium. External surface smooth, with fine con- 

 centric lines visible 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 Inroad, 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 spondyliuni, which is sup- 

 ported, near its apical jwrtion, 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, toward the posterior extremity, probably always 

 do; but anteriorly they become free, forming a spondyliuni, which is sujiported liy a 

 median sejitum 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 spondyliuni. 



Type. — Syntrophia lateralis, Whitfield (sp. ). 



Ohsewations. — Messrs. Hall and Clarke referred Orthh harabuensis 

 and Triplesia primordialis among Cambrian species to Synthrophia 

 and of Ordovician species, Trij^le^la lateralis., StricMandtnla ? arethum, 

 S. ? arachne and (Jauiardla, ealclfera. 



Orthis ? arvuKla Billings, of the Lower Ordovician, certainly has a 

 close resemblance in the spondyliuni of the ventral valve to this genus, 

 and it may represent a radially striated form, as suggested b}" Messrs. 

 Hall and Clarke." Of the relations of the shells referred to Syn- 



"I'al. N. Y., VIII, Pt. 2, p. 218. 



