10 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



Plica. — See Fold. 



Plicate (pi. 24, fig. 5). — Used of a shell that has undulations affecting both the interior and 

 outer surfaces. The primary ornamentation is superposed over the plications. Example: Enteletes. 



Posterior region. — That portion of the shell back of the transverse axis and toward the beak, 

 or apex. 



Procline. — See Pt. Ill, Interareas, and t. fig. 1. 



Protegulum. — The initial shell of all brachiopods. 



Pseudocruralium. — See Notothyrial platform. 



Pseudoresupinate. — See Resupinate. 



PsEUDOspoNDYLiuM (pi. A, fig. 11} pi. 18, figs. 13, 14, 18, 24). — ^A callus resembling a 

 spondylium, developed in some shells beneath the muscles of the ventral valve and confluent with 

 the inner lower surfaces of the dental lamellse. Examples: Glossorthis, Finkelnburgia, Linoporella. 



Punct;e. — Any minute perforations of the test. Punctse are here divided into two kinds: 

 Endopunct;e, perforations of the internal shell layer, never reaching the exterior unless the thin 

 outer shell layer is abraded; these are the typical punctse of the terebratulids and the Dalmanellacea. 

 ExopuNCT^, perforations that indent the external surface of the shell but do not pass through to the 

 interior; well developed in Paurorthis, Hebertellay and Valcourea. 



Recti marginate. — Having a straight anterior commissure. 



Resupinate. — ^A condition wherein the relative convexity of the two valves is reversed, the 

 convex ventral valve of the early growth stages becoming concave and the concave dorsal valve 

 becoming strongly convex, producing thereby a convexo-concave shell. Strictly speaking, this con- 

 dition has never been attained by the orthids, but a few genera simulate it closely, e. g., Valcourea, 

 Dinorthis, Plcesiomys, Hebertella, etc. This latter condition might be called Pseudoresupinate. 



Rostrate. — Having a long beak, produced by narrowing of the hinge-line, as in Conchidium, 

 Cycloccelia, etc. 



Septum. — See Dorsal median ridge, and Median septum. 



Sessile cruralium. — See Cruralium. 



Sessile spondylium. — ^A spondylium which rests directly on the floor of the valve without the 

 support of a median ridge. Nearly attained in Pahlenella. See Spondyloid. 



Shaft. — The stalk or shaft of the cardinal process, which bears the myophore or seat of 

 diductor muscle attachment. 



Sinus. — See Sulcus. 



Sockets. — ^There are sockets for articulation in both valves. In the ventral, there are two 

 kinds associated closely with the teeth: Accessory dental sockets, on the outside of the teeth; and 

 Crural fossettes or sockets {q. v.) on their inner sides. See t. fig. 2. 



Spondylium (pi. A, fig. 9). — A spoon-shaped plate, terminating more or less freely, located 

 in the apex of the ventral valve of various stocks of articulate brachiopods. This plate serves as the 

 seat of attachment of the muscles. It is supported by a more or less elevated, long or short, median 

 septum. Kozlowski has recently shown (1929) that the spondylium may be divided into three 

 different types, as follows: 



Spondylium discretum (pi. 14, fig. 20). — Here the dental plates do not converge and unite 

 medially, but extend directly to the floor of the valve. Strictly speaking, this is not a spondylium, 

 but such a condition of the dental plates is primitive and deserves a designation. This structure occurs 

 mostly in orthids. Also see pi. 18, figs. 13, 14, 1 8. 



Spondylium duplex. — See below. 



Spondylium simplex (pi. 7, fig. 31). — ^A term applied by Kozlowski to the type of spondy- 

 lium in CUtambonites, in which the dental plates and the vertical septum are united into a single 

 piece. This type is in contrast to the Spondylium duplex of Pentamerus (pi. 25, fig. 43), which is 

 composed of two pieces each of which is borne on a basal septum. See Pseudospondylium. 



