GENERA OF THE SUBORDER PENTAMEROIDEA 



159 



For these reasons they included in the genus many 

 similar species, making, as we now see, a rather hetef- 

 ogeneous lot of shells. Since Triplesui lateralis is the 

 genotype, the name must be based upon it, and as so 

 restricted, all of the other species formerly placed here 

 must be taken out of the genus. 



Specimens of Syntrophui are exceedingly rare and 

 none were available to us for sectioning. It is therefore 

 not known with certainty whether the genus possessed 

 a spondylium simplex or one of the duplex type. 

 Polished specimens in the National Museum at Wash- 

 ington do not show a suture line in the septum of the 

 spondylium, hence the presumption is that the latter 

 was of the simplex type, 



? Genus SWANTONIA Walcott 1905 



Walcott, Proc. U. 

 Camb. Brach. 



S. Nat. Mus., vol. 28, 1905, p. 296; 

 1912, p. 796, pi. 104, figs. 5-5b. 



Genoholotype. — Camerella antiquata Billings 

 1861, Pal. Foss., vol. 1, pp. 10-11, fig. 13. 



Description. Exterior. — The species and genus 

 are based on a single ventral valve. Shell ovate, mod- 

 erately convex, subrostrate, with a shallow sulcus 

 toward the front; multicostate (8-12 costs). Inter- 

 area narrow and long; delthyrium open; teeth rudi- 

 mentary, muscle-scars not preserved. 



Geologic range. — Lower Cambrian of Swanton, 

 Vermont (S. antiquata (Billings) 1861) and Nevada 

 {S. weeksi Wz\coK 1905). 



Discussion. — There is some superficial resemblance 

 here to Camerella, but the internal structure is very 

 different. According to Walcott, S. antiquata has a 

 "narrow, strong, concave shelf or area; the area or 

 shelf is free from contact with the bottom of the 

 valve, a recess or chamber existing beneath it." This 

 feature he has taken to indicate a free spondylium, but 

 the presence of such a structure may be questioned. 

 The specimen is preserved as a mold of the interior. 

 In the vicinity of the beak the specimen is indented 

 on each side, the indentation representing the position 

 of the lateral interareas. Immediately under the beak, 

 however, there is no excavation such as would be ex- 

 pected if there were a free spondylium, and the internal 

 mold is united to the matrix rock just as if there were 

 an open delthyrium now filled up. Were it not for 

 the strong costje on the outside of the shell, the posi- 

 tion of Swantonia among articulate brachiopods might 

 be questioned. 



Swantonia therefore appears to be a narrow-hinged 

 form without a spondylium, but its family position can 

 not at present be determined, especially in the absence 

 of any knowledge of the dorsal valve. S. weeksi is 

 also based on a single ventral valve, and shows external 

 characters only. However, as Walcott referred the 

 genus to the Syntrophiida:, we will leave it here 

 provisionally. 



Family HUENELLID^ Schuchert and 

 Cooper 1931 



Syntrophiacea externally like Syntrofhia but costate 

 or costcllatc. Ventral valve with a pseudospondylium ; 

 dorsal brachiophore plates discrete, subparallel. 



Geologic range. — Upper Cambrian and Ozar- 

 kian. 



Embraces but two genera, Huenella Walcott and 

 Huenellina Schuchert and Cooper. 



Genus HUENELLA Walcott 1908 



T. fig. 24 



Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 109; 

 Camb. Brach., 1912, p. 804, pi. 103, figs. 1-li. 



Genoholotype. — Syntrofhia iexana Walcott 

 1905, Proc. U. S. Nat. Mus., vol. 28, p. 294. 



Description. Exterior. — Subelliptical in outline; 

 hinge-line straight, always narrower than the total 

 width of the valves; cardinal extremities rounded. 

 Lateral profile biconvex. Anterior commissure unipli- 

 cate; dorsal fold broad in front, prominent; sulcus 

 deep. Ventral interarea longer than the dorsal, apsa- 

 cline, delthyrium open ; dorsal interarea anacline, noto- 

 thyrium open. Surface costate or costellate, especially 

 toward the front. Test fibrous (?), impunctate. 



Ventral interior. — Delthyrial cavity deep ; teeth 

 strong and somewhat elongate; dental plates well 

 developed, converging to the floor of the valve to form 

 a pseudospondylium which bears the muscle-scars. 

 Two broad paUial trunks diverge antero-laterally from 

 either side of the pseudospondylium and follow the 

 shell sulci nearly to the front margin. 



Dorsal interior. — Notothyrial cavity deep; brachio- 

 phore supports short, convergent, but cemented directly 

 to the floor of the valve. At the anterior they are 

 extended forward and laterally as low ridges which 

 separate the anterior from the posterior adductor scars. 

 Cardinal process simple, very faintly visible or absent. 

 Adductor impressions elongate, tear-shaped or oval, 

 directed antero-laterally. A pallial sinus is given off 

 from the anterior extremity of each adductor impres- 

 sion. The inner trunks extend along the margins of 

 the sulcus, while the outside trunks pass .ilong the 

 anterior portion of the lateral lobes. 



Geologic range. — Upper Cambrian and Ozar- 

 kian of North America. 



Species 



Costate section 



Huenella ainormis {W ikon) 1905 

 H.iillingii (Walcott) 1905 

 //. A^rj Walcott 1924 

 H. Iexana (Wilcon) 1905 

 H.texanalttviusculus iyizXcoxx) 1905 



