GENERA OF THE SUBORDER ORTHOIDEA 



109 



iophores arc likewise orthoid and supported by adven- 

 titious shell deposited on their inner and dorsal surfaces. 

 This adventitious material may be extended laterally 

 for some distance (see D. dice (VValcott)) so that the 

 cardinalia of Deltatretn resemble markedly those of 

 Citttimhonites. The median ridge given off from the 

 notothyrial platform extends nearly to the middle of 

 the valves as is usual in orthoid shells. The sockets 

 are the cavities formed by the envelopment of the 

 brachiophores by adventitious substance and by the 

 sloping outer face of the brachiophore. 



Deitatreta, like many orthoid brachiopods, possesses 

 an incomplete chilidium composed of two discrete chi- 

 lidial plates. These are low, extending from the mar- 

 gins of the notothyrium, and covering its sides; they 

 are extensions built on the edges of the brachiophores 

 along the delthyrial margins and strengthened by ad- 

 ventitious shell deposited on the inner face of the 

 brachiophores. The specimens at hand are not favor- 

 ably enough preserved to show the dorsal musculature. 



This discussion of the genus Deitatreta has been pre- 

 pared from material loaned by Dr. E. O. Ulrich and 

 the U. S. National Museum. The specimens are all 

 from the upper Canadian of Alabama and Oklahoma. 

 We also include in this genus Billingsella dice Walcott, 

 found in the drift near St. Albans, Vermont, which is 

 very close to Deitatreta^ n. sp. (see pi. 6, fig. 1 5 ) from 

 northeast of the Wichita Mountains, Oklahoma. 



Turning now to the nomenclatorial difficulties, the 

 first use of the name Deitatreta was by Ulrich in a 

 faunal list prepared by him for Purdue and Miser,'* 

 the name appearing as "Deitatreta of. electro Billings" 

 and unaccompanied by any description or figure. This 

 citation is then clearly a nonien nudum and as such has 

 no standing.*" 



In 1926 Butts used Deitatreta as of Ulrich for 

 shells collected in Alabama and Oklahoma. Two 

 species were named and both were accompanied by 

 illustrations and one of these has a short statement of 

 Ulrich's conception of the genus. Since no type has 

 ever been definitely designated for Deitatreta, we here 

 select D. fillistriata Butts. This species has been chosen 

 instead of D. elegantula Butts which appears first in 

 the report (page 99, in reference to the figures on 

 plate 18), because there is no characterization of the 

 latter species and in addition it is clearly not typical 

 of Deitatreta according to the views expressed for D. 

 fdlistriata and as indicated by Ulrich's specimens in 

 Washington. In the plate legend (pi. 18, figs. 1-4 

 [p. 100]) for D. fillistriata, Butts states clearly that 



"U. S. Geol. Surv., Geol. Folio 202, 1916, p. 5. 



"* The recent Schuchert-LeVcne catalogue cites the geno- 

 type as "D. cf. electra Ulrich ? = Orlhis electra Billings," 

 with bibliographic reference to the last named species. 

 Since, however, the name as written by Ulrich is a doubt- 

 ful identification, it can not be held that he intended to 

 place Billings' species as the type of the genus. See Rules 

 of Nomenclature, Art. 30, 11 e^. 



Ulrich has proposed the name Deitatreta for shells 

 having a deltidium. Hence D. elegantula, which has 

 no deltidium, is obviously not typical of Deitatreta as 

 conceived of by Ulrich. We refer it doubtfully to our 

 new genus Paurorthis. 



Genus POMATOTREMA Ulrich and Cooper, 

 n. gen. 



(Gr. pntna, cover; trciiia, hole) 



PI. 16, figs. 14-16, 18-21,23, 26,31 



Genoholotype. — p. muralis Ulrich and Cooper, 

 n. sp. 



Discussion. — On plate 16 the writers figure a shell 

 that has been known as "Orthisina" grandcrva, being 

 first referred to Orthisina and later by Hall and Clarke 

 to Billingsella. However, it does not belong to either 

 of these, but is of a new genus which is not uncommon 

 in the Lower Ordovician. We had provisionally re- 

 ferred this species to Tafia, but after the junior author 

 had studied interiors of the genotype, Taffia planocon- 

 vexa, at Washington (unfigured by Butts) he found 

 that the group under consideration {Pomatotrema) has 

 nothing to do with Taffia as figured by Butts. It was 

 Ulrich's intention to affix the name Taffia to shells 

 similar to if not identical with O. granda-va, but in the 

 Alabama report unfortunately T. flanoconvexa was 

 figured and this of course fixed the genotype of Taffia. 

 Being so established, Taffia is not congeneric with 

 Orthisina gratidcrva, but is a member of the family 

 Orthidas. 



The junior author discovered the differences be- 

 tween Taffia and Pomatotrema after he had removed 

 from Yale University to the U. S. National Museum, 

 and after he had agreed to collaborate with Dr. E. O. 

 Ulrich in a study of the Ozarkian and Canadian 

 brachiopods. Consequently the new genus Pomato- 

 tre7na born by the above union bears as its author the 

 names Ulrich and Cooper, with P. muralis Ulrich and 

 Cooper as the genoholotype. The following discus- 

 sion of the genus is based on material in the U. S. 

 National Museum and the figured specimens from 

 Newfoundland in the Schuchcrt Collection at Yale. 



Distinguishing characters. — Plano-convex in 

 lateral profile, with perforate deltidium, chilidial plates, 

 and subparallel or vcntrally convergent dental plates. 



Pomatotrema muralis Ulrich and Cooper, n. sp. 



PI. 16, figs. 15, 20 



Shell small or medium-sized, nearly as wide as long, 

 cardinal extremities nearly a right angle. Ventral 

 interarea long; delthyrium longer than wide, covered 

 by a prominent convex deltidium which is apically per- 

 forate as in Vellamo. Notothyrium partially closed by 

 chilidial plates. Surface multicostellate, about 3 cos- 

 tellae to 1 millimeter at the front of the shell. Dental 



