BRACHIOPODA. 63 



narrow, divergent muscular grooves, bordered on their anterior edges by thick- 

 ened ridges, both having the shape of a broad inverted V. 



In the brachial valve the character of the hinge-plate has not been ascer- 

 tained, but was probably simple, and it was supported by a median septum 

 traversing about one-half the length of the valve; on either side of this septum 

 are the lateral members of the adductor impression. The crura are short and 

 straight ; the primary lamellae are attached to them by a subrectangular curve 

 and pass outward just within the margin of the valve. The spirals are but 

 slightly elevated and have their apices directed outward toward the lateral 

 slopes of the opposite valve. The ribbon makes but three or four turns, and 

 its outer anterior edges are quite coarsely fimbriated. The loop is situated 

 anteriorly, taking its origin near the upward turn of the primary lamellae ; it 

 is directed upward and backward, the lateral processes meeting at or just behind 

 the center of the interior cavity. From the point of union proceeds a short, 

 simple process, which does not make an angle with the rest of the loop. 



We have had the opportunity of verifying most of these characters by 

 cuttings of specimens obtained from the Gotland limestone. No congeneric 

 species was known to Mr. Davidson, and, as far as our knowledge goes, there 

 is no representative of this structure in the American palaeozoic faunas. 



The external resemblance of Dayia navicula to the Atrypa bisulcata of the 

 Trenton limestone, is worthy of remark, and the differences between the two 

 in the structure of the brachidium are actually slight, though in one the spirals 

 are everted and in the other they are inverted. Further notice is taken of 

 these differences in the discussion of the genus Cvclospira. 



Genus H IN DEL LA, Davidson. 1882. 



PLATE XLI. 



1862. Athyrit, B1U.INO8. Palffiozoic Fossils, vol. i, p. 144, fig. 121 ; p. 145, fig. 122. 



1863. AthyrU, BiLUvaa. Geology of Canada, p. 317, fig. 331. 



1882. Hindella, Davidsos. Bi-ilish Silurian Bi-achiopoda, Supplement, p. 130. 

 188.5. Meritttlla, Kokrotr. Bull. Denison Univei-sity, vol. i, p. 88, pi. xiii, fig. 2. 



Mr. Davidson has found that the meristelloid species described by Billings, 

 from Junction Cliff, Anticosti (Division 1 of the Anticosti group), as Athyris 



