201 



Interior. The cardinal area is high and has about seven furrows whioh 

 are arched forward at the sides to the deltidial ridges (b) ; the areal 

 borders (a) are thick and flattened. A small umbonal muscle scar ? (c) is 

 found just within the hinge-line ; but at the sides of the area within the 

 body cavity are stronger prints (d) which may be interpreted as paired 

 cardinal scars or perhaps transmedian scars. The central muscles (A) are 

 about two-fifths of the length of the valve from the back, and are rather 

 close together ; and the anterior laterals (j) are nearly as far forward as 

 the mid length of the valve ; a median septum (i) divides both pairs of 

 muscle scars ; there is a faintly marked median sinus (m) in the anterior 

 third of the valve. The transmedian muscle scars (g) are small compared 

 with those of most species of Lingulella and nearly as far forward as the 

 centrals (A). Two small scars behind the transmedian appear to be those 

 of the I and k laterals. Faint impressions of the vascular trunks (k) ex- 

 tend forward in a regular arch, rather near the margin of the valve. 



The central scars in this valve are approximated as in Lingulella, not 

 spread as in Obolus. 



The surface of the callus shows abundant pitting as in Lingulella 

 Davisii and other species of Lingulella and Lingulepis. 



/Sculpture. The surface of the valves is shining and smooth, except for 

 shallow crescent- shaped grooves and more distinct growth lines ; these are 

 more distinct on the lateral and front margins than elsewhere. Besides 

 these markings, a strong lens reveals a minute granulation all over the 

 surface. 



Size. Length of the ventral valve (from St. John), 21 mm.; width. 16 

 mm ; length of the dorsal (from Escasonie), 17 mm.; width, 14 mm. 



Horizon and locality. From layers of fine sandy shale of Div. 3a. 



Salters' original figure of L. Davisii in the Memoirs of the Geological Compared 

 Survey of Great Britain, shows that that species like this one, was pitted 

 over the visceral region,* and it is nearly of the size of these shells, but 

 these do not exhibit the " satchel shape," supposed to be characteristic 

 of that species, and which we find in the species next described from a 

 higher horizon. (See page 203). 



The position of the muscle marks in these valves may be compared with 

 those of L. Davisii as figured by Mr. Walcott.f 



VAR. LENS, PI. XV, figs. 3a-h. 



Lingula (?) lens Bull Nat. Hist. Soc. of K B., vol. IV, page 274, pi. 

 V, figs. 3 a to A. 



*Mem. Geol. Surv. Great Britain, vol. 3, pi. 2 fig. 11 a and pi. 4, figs. 14 and 14 o. 

 fU.S. Nat. Mus. Proced. vol. XXI, pi. XXVII figs. 1 and 2. 



