CLASSIFICATION OF THE BRACHIOPODA. 85 



imperforated,^ incurved, and in general overlying the umbo of the smaller valve ; no area 

 or defined beak ridges ; valves articulating by teeth and sockets ; external surface com- 

 monly smooth. In the interior of larger or ventral valve the dental plates are fixed to, 

 and along the sides of a longitudinal prominence or convex, arch-shaped plate, which ex- 

 tends to less than a third of the length of the shell, with its narrow end fitting into the 

 extremity of the beak, and its lateral diverging edges to the bottom of the valve. In 

 the free medio-longitudinal region, between the gradually declining base, or prolongations 

 of the condyle plates, were situated the cardinal and adductor muscles ; this last has left a 

 small, elongated, heart-shaped scar, under and along the outer sides of which are seen 

 the much larger oval impressions of the cardinal muscles. The interior of the smaller 

 or dorsal valve is partly divided by a large, deep, longitudinal septum, which extends 

 from the extremity of the umbo to about two-thirds of the length of the shell, sup- 

 porting at its origin the hinge-plate, which is divided into two portions by a narrow 

 gradually widening channel; to the socket ridges are affixed the spiral cones, the ex- 

 tremities of which are directed towards the lateral margin of the shell ; on either side of 

 the septum are seen two muscular scars formed by the adductor. 



Obs. I felt greatly embarrassed as to the course advisable to pursue relative to the 

 name Athyris proposed by Professor M'Coy for a few species which do not always agree 

 with the derivation of the term, or with the short undetailed diagnosis then published, viz., 

 ^'nearly orbicular, small; no cardinal area or hinge line ; spiral appendages very large, 

 falling the greater part of the shell!' The author names several examples, of which some 

 are decidedly perforated, T. concentrica (De Buch) ; others apparently not so, while a few 

 belong to the genus Spirifer of Sow. ; it is true the Professor had then the erroneous 

 belief that his first-named type ichen perfect^ was imperforated, and therefore gave to his 

 section a name implying such a condition. In 1847, M. d'Orbigny objected to the de- 

 nomination, stating it to be "^;^ complete contradiction with the zoological characters''^ ?c(\^ 

 proposed as a substitute the name Spirigera — T. concentrica of Baron de Buch, being his 

 type. Shortly before (1835 or 1836), Professor King having received from the Eifel a 

 specimen labelled T, concentrica^ but which was really an example of T. scalprum, 

 erroneously described the Baron's species ''with condyle plates attached to a process resem- 

 bling a shoe lifter;"* impressed with that idea, and justly perceiving certain important 

 differences in a Permian species {T. pectinifera), he proposed for this last a separate generic 



' Although no well-defined foramen is visible in the generality of half grown or adult individuals, 

 I have clearly traced the existence of a small circular aperture in some young exiimples, which no doubt 

 became cicatrized, and dispensed with at a more advanced period of the animal's life. 



2 Paleont. Fran9. Ter. Cretaccs, vol. iv, p. 357, 1847. 



3 Professor King having most obligingly forwarded for my inspection his so-called T. concentrica, 

 I at once recognised in it a well-known Eifel species, T. scalprum of Roemer. 



* Ann. and Mag. of Nat. Hist., vol. xviii, p. 86, 1846, in that paper Professor King ably describes the 

 remarkable process above mentioned. 



