258 DUBLIN UNIVERSITY 



supports ;* and, that their form and arrangement, in different fami- 

 lies, constituted generic diagnoses, as is the case with the teeth in La- 

 mellibranchs. I have therefore been led to institute two of the follow- 

 ing genera on the peculiarities of their muscular fulcra : — 



Family.— TEREBRATULID^l. 



Diagnosis. — Small valve, generally furnished with a short, slightly 

 recurved or anneliform loop, having its crura attached, one to each of the 

 dental protuberances, and supporting the origin or basal portion of the 

 labial appendages. 



This family includes Terebratula, Terebratulina, and some other 

 genera, one of which I consider is the genus next to be described. All 

 of them appear to be entirely devoid of the muscle-bearing shelly plates 

 common in the next family, and others (Rhynchonellidae, &c.) belonging 

 to the Helictobrachiate order. The want of these shelly plates constitutes 

 a negative character of much importance in the present family. 



Genus. — Gwynia {King). 



Diagnosis. — Smooth, subequivalved, sub-auriculated and longitu- 

 dinally oval : valves thin, with both umbones prominent : foramen 

 emarginated by the deltidial fissure : teeth strong, lamelliform, rather 

 apart, and situated on the sub -auricles : cardinal muscular fulcrum ex- 

 cavated in the substance of the large plate : labial appendages free, 

 except at their origin, where they are directly attached to the surface 

 of the shell : perforations in the shell tissue rather large and wide apart. 



Type species. — Terebratula capsula {Jeffreys). — The present genus 

 is founded on a very minute shell, first discovered by Mr. J. Gwyn 

 Jeffreys (to whom I have, with much pleasure, dedicated it) at Etretat, 

 on the coast of Normandy, and since determined by him as occurring 

 in Belfast Lough, where it has been taken by Messrs. Hyndman and 

 Norman. Mr. Jeffreys, in his account of the species (vide " Annals of 

 Natural History," January, 1859), remarks: — " This shell being equi- 

 valve, or nearly so, it may be a question whether it ought not to be 



* The "pedicle muscles" generally. But the "valvular muscles" also, in Camaro- 

 phoria, appear to have been supported by the spatula-shaped process of this genus ; and 

 a like office has apparently been subserved by the two long vertical plates in the small 

 valve of Pentamerus. 



