DEFINITIONS OF BRACHIOPOD TERMS 1 1 



Spondyloid (pi. 14, fig. 8). — In this condition the dental plates are so thickened on their inner 

 basal sides that the added testaceous deposit grows together and simulates a spondylium. This con- 

 trasts with the pseudospondylium, which is formed by a callous thickening on the floor of the valve. 

 Example : Porambonttes. 



Stride. — Interspaces between costx and costellae. This term has been much abused and its 

 current use for a radial rib is incorrect. 



Sulcus (sulcate). — A median depression in the convexity of the shell, the opposite of a fold 

 or plica. Replaces the term sinus. 



Teeth (pi. A, fig. 2). — The two articulating processes of the ventral valve. There are also 

 accessory small teeth in the dorsal valve in many brachiopods, which are here called Denticles 

 {q.v.). 



Transverse axis. — A line through the widest part of the shell from left to right. 



Umbonal cavities. — Chambers separating the dental lamellas from the walls of the valve. 



Uniplicate. — A term applied to the anterior commissure when there is a fold in the dorsal 

 valve opposed by a sulcus in the ventral valve. Unisulcate is the reverse condition. 



Unisulcate. — See Uniplicate. 



Ventral dental sockets (pi. A, fig. 2). — Small sockets in the teeth of the ventral valve next 

 to the hinge margin. Into these articulate small denticles on the outer wall of the dental socket. 

 They are also called Accessory dental sockets. See Denticles. 



Ventral valve. — The shell situated on the ventral side of the animal, and in articulate forms 

 having the teeth on each side of the delthyrium. Usually the larger and deeper of the two valves. 

 Pedicle and Dental are other names applied to it. 



