BRACHIOPODA. 101 



ij. Tetractinella includes forms with four ribs on each valve. 

 6.,. Pentactinella includes those with five ribs on each valve. 

 6.5. Anomactinella includes those with a number of ribs sharply de- 

 veloped toward the margin. 



2. Amphitomella ; smooth shells with a very strong cardinal plate, and a 



median septum in each valve extending the entire length of the shell 

 and dividing the cavity into two chambers. 



3. Dioristella; smooth shells having a loop whose lateral branches return 



upon themselves, somewhat as in Meristella. 



Genus KAYSERIA, Davidson. 1882. 



PLATE XLI. 



1841. Orthis, Phillips. Palaeozoic Fossils Cornwall, Devon and West Somerset, p. 65, pi. xxvi, tig-. 110. 



1842. Orthis, d'Archiac and de Vekneuil. Descr. Older Deposits Rhenisii Provinces ; Trans. Geo!. 



Society, London, sec. ser., vol. vi, p. 396. 

 1853. Orthis, Steininger. Geog-n. Beschreibung- der Eifel, p. 80, pi. v, tig. 5. 

 1864. Atrypa, Davidson. British Devonian Brachiopoda, p. 51, pi. x, fig. 1. 

 1871. Retzia, Quenstedt. Petret'actenkunde Deutschlands ; Brachiopoden, pi. li, tigs. 21-25. 

 1871. Retzia, Katser. Zeit.sch. der deutsch. geolog. Gesellsch., vol. xxiii, p. 161. 

 1882. Kayseria, Davidson. Devonian Brachiopoda, Supplement, p.'21, pi. ii, figs. 11, 12. 



Orthis lens, Phillips, the type-species of this genus, is a small middle Devonian 

 shell, with depressed-conve.x or lenticular valves, radially plicated exterior, 

 and a median plicated sinus on both valves. Its external expression is not unlike 

 that of some of the retziiform species which belong to the genus Rhynchospira, 

 though it possesses an impunctate shell. The complicated internal organiza- 

 tion has been elaborated by the Rev. Norman Glass and described at length by 

 Mr. Davidson. The pedicle-valve bears a low, thickened median ridge, but is 

 otherwise devoid of pronounced peculiarities. In the brachial valve there is a 

 high median septum which arises from beneath the divided hinge-plate and 

 reaches its greatest elevation at a point behind the center of the valve, whence 

 it descends rather abruptly, traversing altogether about two-thirds the length 

 of the valve. 



The spiral cones form sharp angles with the crura, and are directed laterally ; 

 the loop is very stout, taking its origin at about one-third the length of the 



