6% INTRODUCTION. 



Genus — Terebratula, Llhwyd, 1696.^ 



Ty]pe — T. viteea, lAnn., sp. Introduction, PI. VI, figs. 1 — 4. 



Concha Anomia, (part) Columna, 1606 and 1616. 



Anomia, (part) of Linnceus, Gmelin, Da Costa, ^c. 



Terebratula, (part) Llhwyd, and the generality of authors. 



Lampas, (part) of Humph. 



Gryphus, Me^er/e, 1811. Philippi, 1853. 



Terebratulites, (part) of Schloth. 



Pygope (diphya), Link. 



TEREBBATULiE, "witli short loops, Dav. 



Epithybis (elongata), King. 



Antinomya (diphya), Catullo. 



Shell, oval, elongated, or transverse, externally smooth or plaited, valves more or less 

 Fig. 2. Fig. 3. unequally convex, margin even or waved : hinge line 



curved, beak short, truncated by a foramen, variable 

 in size, and partly margined by a deltidium in one or 

 tvi^o pieces ; loop short, confined to the posterior por- 

 tion of the shell, and not exceeding much more than 

 a third of the length of the valve, simply attached 

 Ter. vitrea. to tlic hiugc platc. The two riband-shapcd lamella 



. orsa va ve s owing le oop. ^^^ ^^^^ united by a transvcrsc lamella, bent upwards 



3. Dorsal valve with the animal ; the oesophagus ^ ^ 



passes through the opening of the loop. in the middle. The cirratcd arms are supported by the 



crura, and project considerably in front of the loop : no internal septum in the socket valve. 

 Ods. Some Palaeontologists^ seem disposed to consider the species with short loops as 

 the types of the genus Terebratula, and propose to place into separate sections or sub- 

 sections those forms in which the calcified supports extended to near the margin before 

 becoming reflected {Waldheimia), as well as those in which the crura unite in the form of a 

 band behind the mouth of the animal {Terehratnlind) ; but these sub-divisions, if of little 

 essential value, are very convenient in the arrangement of the species, which may even be 

 distinguished by external characters : thus in those forms with long loops, the mesial 

 septum may easily be traced on the external surface of the smaller or dorsal valve,^ while 

 none such occurs in the short-looped species. 



The genus Terebratula, as here limited, includes a vast number of species, more than a 

 hundred having been described and figured. The dimension of the foramen is very 

 variable, being sometimes so large as almost to admit the end of a finger, {Ter. grandis) 

 while at other times it will hardly afibrd space for the passage of a hair. {Ter. carnea.) 



1 Llhwyd; Lith. Brit. Ichn., 1696, Terebratula minor subruhra, pi. ii, fig. 890 = T. maxillata, Sowerby. 

 - This view is adopted by Professor King, Dr. Gray, Mr. Woodward, and others. 



•'' This occurrence was first observed by M. Deslongchamps ; the length of the septum may easily be 

 ascertained by the use of a little acid. 



