GENERA OF THE SUBORDER ORTHOIDEA 



47 



Species 



BillingseUa billingsi (Hartt) 1868 

 B. latourensis (Matthew) 1886 

 B. quacoensi4 {M.M\\ev;) 1886 



? Eoorthis /uutingsensis Walcott 1905 



P. (?) hunnehergensis and P. wingi of Walcott can 

 not be placed in any Cambrian genus. P. helcna and 

 P. l/Fvis of the same author may be syntrophiid. 



More recently, Walcott'' has also referred two 

 Ordovician shells, P. tones and P. porcias, to this genus. 

 Neither has a free spondylium or any structure ap- 

 proaching it. Furthermore, both species are compos- 

 ite, including representatives of Archceorthis and prob- 

 ably of Tafia. 



Distinguishing characters. — Protorthis extern- 

 ally resembles Eoorthis with its rather large costells, 

 but the unsupported short spondylium of the ventral 

 valve is an important feature in its identification. 



Discussion. — The preservation of the New Bruns- 

 wick Middle Cambrian Protorthis is not good. The 

 specimens occur in a soft and much distorted shale and 

 accordingly are much crushed. It is, however, possible 

 to distinguish, in molds of the interior, rather small 

 teeth for articulation of the valves, and thickenings 

 along the delthyrial margins which are the tracks of the 

 forward growth of the teeth. 



The most interesting and important internal feature 

 in Protorthis is the very short and small spondylium 

 that hangs free in the delthyrium. Hall and Clarke' 

 say correctly that the cardinal area "is transected by a 

 broad delthyrium which is closed below by a concave 

 plate apparently produced by the union of the dental 

 lamelLx, which are not continued to the bottom of the 

 valve." In Protorthis the spondylium is variable in 

 length ; in some species it is a narrow shelf under the 

 posterior lateral margins of the delthyrium, and in 

 others it is a spoon-shaped plate two-thirds the length 

 of the delthyrium. Since the function of the true 

 spondylium is to furnish attachment for the diductor 

 and adductor muscles, one should expect to find scars 

 on the spoonlike plate. No such scars have been seen 

 on the spondylium, nor have definite scars been dis- 

 covered on the floor of the valve beneath the spondyl- 

 ium. Evidence is therefore lacking as to the function 

 of this peculiar structure. Such a plate as this is un- 

 known elsewhere among the orthids. Among the 

 pentamerids a free spondylium is known and its origin 

 can be traced to the resorption of the median support- 

 ing septum. Such an origin can not be maintained for 

 the spondylium of Protorthis because there is no known 

 spondylium-bearing (with a median septum) ancestor 



< Smiths. Misc. Coll., vol. 67, no. 9, 1924, pp. 503, 

 504. 



'Pal. N. Y., vol. 8, pt. 1, 1892, p. 231. 



from which it could have been developed. Further- 

 more, the orthoid brachiopods older than Protorthis 

 were not provided with dental lamells. It is here sug- 

 gested that in Protorthis we have one of the earliest 

 developments of dental plates, but in this instance the 

 dental lamella: grew toward each other and united 

 instead of growing directly ventrally to the floor of 

 the valve. 



The morphology of the dorsal valve of Protorthis is 

 not unlike that of Nisusia and BilUngsrlln, since the 

 former has very primitive cardinalia and a cardinal 

 process is wanting. No definite evidence of the mus- 

 culature is known. 



It has been customary, since the publication of Prot- 

 orthis by Hall and Clarke, to say that it has a punctate 

 shell. The evidence for this statement is found in the 

 presence of fine papillx on the molds of the exterior or 

 interior. Although papilla? are suggestive of punctje, 

 a thin section of the shell in the Schuchert Collection 

 fails to reveal true puncta; (endopunctas). On the 

 other hand, as no Cambrian articulate brachiopod is 

 definitely known to have a punctate shell (endopunc- 

 tate), it is hardly to be expected that Protorthis has 

 such. 



Protorthis is unlike any other known genus and 

 therefore appears to be an early specializing stock 

 which gave rise to no other groups. 



Genus LOPERIA Walcott 1905 



Walcott, Proc. U. S. Nat. Mus., vol. 28, 1905, p. 287; 

 Camb. Brach., I9I2, p. 744, pi. 99, figs. 5-5j. 



Genoholotype. — Protorthis (Loprria) dougald- 

 ensis Walcott 1905. 



Description. Exterior. — Outline subquadrate, 

 hinge-line straight, cardinal extremities obtusely sub- 

 angular; lateral profile resupinate. Ventral interarea 

 long, strongly apsacline; delthyrium open. Dorsal 

 interarea short, procline or faintly anacline; notothy- 

 rium narrow, open. Surface multicostellate. Micro- 

 structure probably fibrous impunctate. 



Ventral interior. — Precisely as in Protorthis. 



Dorsal interior. — Crural bases very short, nototh)'- 

 rial platform small, bearing a very low, thick cardinal 

 process. Median elevation low. 



Geologic range. — Middle Cambrian. Only 

 known species, L. dougaldensis Walcott of Cape 

 Breton, Canada. 



Distinguishing characters. — Loperia is charac- 

 terized by the same internal features as Protorthis, but 

 differs in having a strophomenoid lateral profile or con- 

 vexo-concave shell. The ventral valve has strong 

 teeth and a free spondylium, but no clear evidence of 

 musculature was seen on it. In the dorsal valve, the 



