Cu m ings — Iforphogen esis of Platystrophia. 5 



muscular impressions are the same ; many individuals of the 

 Orthis calligramina group manifest a tendency to form a 

 sinus, which, in Platystrophia is so strongly developed that 

 with the corresponding fold of the dorsal valve it constitutes 

 a chief characteristic of this subgenus." It is only necessary 

 to state that the presence of a sinus in the ventral valve of 

 adult Brachiopoda is so nearly universal as to be of little use 

 in tracing phytogenies. As a matter of fact the nepionic shell 

 of Platystrophia has the sinus in the dorsal valve and the fold 

 on the ventral. Though this feature also characterizes many 

 specimens of 0. calligramina^ nevertheless the fact that a dorsal 

 sinus is a nepionic feature of such widely separated forms 

 as Dalmanella, Phynchonella, Phynchotreta, Phynchospira, 

 Coslospira, Atrypa, etc., renders this character of little signifi- 

 cance in indicating a common origin of 0. calligramma and 

 Platystrophia. 



The ancestors of Platystrophia are scarcely to be sought in 

 the Ordovician, since the genus is already represented in the 

 lower beds of this system.* In the Upper Cambrian, however, 

 we meet with a form that possesses in the adult practically all of 

 the nepionic characters of Platystrophia. This form is Orthis 

 lenticularis "Wahlenberg sp., a widely distributed and highly 

 variable species, found in the Lingula-flags of Wales, the Alum 

 schists of Scandinavia, and the equivalent formations of Canada, f 

 Through the kindness of Dr. Gr. F. Matthew I have obtained 

 for examination the types of his var. lyncioicles of this species, 

 from the Upper Cambrian of St. John, !N~. B. These are 

 shown in fig. 1, b and c.% The contour of fig. lb is precisely 



* Platsytrophia has several times been stated to occur in the Chazy of this 

 country, (see Hall and Clarke, Pal. N. Y. , viii, pt. i, p. 202. — Winchell and 

 Schuchert, Geol. Minnesota, iii, pp. 456, 457. — Schuchert, Bull. U. S. Gr. S., 

 No. 87, p. 309; Proc. U.'S. National Museum, vol. xxii, 1900, p. 151 

 (Birdseye). — Ruedeniann, Bull. N. Y. State Museum, No. 49, Dec, 1901, p. 

 92). I am unable to find any original reference in the literature to its occur- 

 rence in rocks of this age. Messrs. Ami, Whiteaves, and W. Billings of Ottawa, 

 Canada, inform me that the museum of the Canadian Survey contains no 

 Chazy specimens ; and that they are not aware that the species has ever been 

 found in that series. Mr. Billings suggests that it may have been found in 

 rocks formerly held as Chazy, but now known to be of later age. Mr. McBride 

 of Montreal writes that there are no Chazy specimens in the museums at 

 Montreal and that he does not know of the occurrence of Platystrophia in the 

 Chazy. Mr. Seely, who is familiar with the Chazy, writes to the same effect. 

 It is very probable therefore that the form is not known to occur below the 

 Trenton in this county. 



f For svnonomv and descriptions of this species see Davidson, Silurian 

 Brachiopoda, 1869, pp. 230-232 :— Matthew, Trans. Roy. Soc, Canada, ix, 

 1891. Sec. iv. pp. 46-49. Wysogorski (Entwicklungsgeschichte, p. 8, foot- 

 note 1) places O. lenticularis in the genus Orthis emend. Wysog., which 

 includes the impunctate Orthidce. 



X These two specimens are figured by Matthew (op. cit., pi. xii. fig. 10). 

 His fig. 106 represents the same individual as our fig. 16. It should be noted 

 that all the plications reach the front margin and several of them bifurcate, 

 giving, as shown in our figure, several additional plications at that point. 



