NO. 1395. CAMBRIAN BRACHTOPODA—WALCOTT. 289 



frojyhia^ to SfyricMandinla^ they consider that the points of structure 

 may represent the strnctui'e which is represented l)y the Sti'liMand!' 

 iiias of the hiter Sihirian and Devonian. Mr. Billings noted the rela- 

 tionship existing between his Gamarella calolfera and Stricklandinia/'- 

 It is probable that S. nrachne^ S. arethnsa, and similar forms should 

 be referred to a distinct genus. They are not typical Stri('khitidiii!ai<^ 

 and they differ in surface and shape from Synirophla late>'alis. 



The Cambrian type of Syntrophia is 8. rotundatus of the Upper 

 Cambrian. It has a spondylium in each valve supported by a median 

 septum, and a short area divided by a large open delthyrium. 



The Middle Cambrian species, S. texana^ and Upper Cambrian 

 species, 8. ahnormis differ from the type species in having the greater 

 portion of the bottom of the spondylium of each valve attached to the 

 bottom of the valve, no evidence of median septum having been found 

 except in a cast of a dorsal valve. 8. primordialh has no median 

 septum in the dorsal valve, in this respect resembling the dorsal valve 

 of CamareUa voJhorthl. There is considerable variation of form in the 

 different species, but this is not much greater than the varieties of the 

 type species, 8. lateralw. 



The species referred to the genus ma}^ be divided into two groups, 

 the plicate and nonplicate. The plicate species begin with aS". te.vmia^ 

 and includes 8. abnormiH^ 8. orientalis, and 8. MlUngsi, all of the 

 Upper Cambrian. The nonplicate or smooth species are 8. alata^ 8. 

 rotiindata^ 8. Ijarabuensis, and 8. prim,ordialis, of the Uppei- Cam- 

 brian, and 8. adcifeni., 8. lateralis, 8. mmdma and allied forms, of 

 the Ordovician. 



SYNTROPHIA ABNORMIS, new species. 

 CamereUa calcifera Meek, .Sixth Ann. Rept. U. S. Geol. Sur. Terr., 1873, p. 464. 



The general form varies from transverse to elongate. Valves bicon- 

 vex, with dorsal very convex in some specimens. Hinge line straight. 

 Surface marked by concentric stria^ and imbricating lines of growth 

 crossed by fine, rounded, radiating stria? and a variable number of 

 rounded ribs; specimens occur with four ribs in the sinus of the ven- 

 tral valve and four on each slope outside the sinus; in other ventral 

 valves only a trace of ribs can be seen. On the dorsal valve there are 

 shells without a sign of ribs, and others with a trace of rib on the 

 median fold to three ribs on the fold and traces on the lateral slopes. 

 The largest shell has a length of 7 mm. ; width 9 nun. ; there is great 

 variation in the proportion of the length to the width. 



The ventral valve has a broad, strong sinus that depresses the front 

 of the valve; area well defined, with a large, open delthyrium. Casts 

 of the interior of the ventral valve show a well-marked spondylium 



«Pal. Foss., I, p. 84. 



