Report of the State Geologist, 551 



rolled; it is concave in the middle and bears on both sides ele- 

 vated crests with sloping Lateral faces; its anterior margin is 

 curved inward, and the whole platform seems to be excai 

 below. From its sides diverge two bifurcating ridges, and a 

 median septum extends nearly to the anterior margin. Near the 

 lateral margins two sharply defined spaces are inclosed by nar- 

 row ridges. The interiors of both valves are marked with radi- 

 ating striae. Shells small ; shell substance veiy thin. 



Type. Lakhmina linguloides, Waagen (sp.). Obolus-beds 

 India (Cambrian). But one species is known. 



Lingulasma, Ulrich. 1889. 

 (Plate 1, Figs. 21-24.) 



Shells large, sub-quadrate, linguliform, sub-equi valve ; the 

 brachial valve considerably the deeper. Beaks apical, cardinal 

 margins gently sloping to the sides. External surface covered 

 with concentric or radiating lines and bead-like granules. Shell 

 substance thick, largely calcareous. 



Interior of the pedicle-valve with a low, concave platform which 

 extends over one-half the length of the shell, and is not hollowed 

 on its anterior wall. The pedicle-area has been largely inclosed 

 within the shell, making a distinct sheath or shelf, beneath which 

 lie the apical portions of the central and lateral muscular scars. 

 Crescentic scars scarcely defined. 



The brachial valve is deep, with a high platform of about the 

 same extent as that on the other valve, sloping inward near its 

 anterior margin and continued axially into a strong septum 

 which reaches nearly to the front of the valve. The anterior 

 walls of the platform are broadly excavated, and close against 

 the base of the septum are hollowed out into short conical cavities. 

 The crescent is strongly developed, sharply pointed backward at 

 its center: Its lateral curves are broad, reaching to the edge of 

 the platform. Directly in front of its central angle lies a short, 

 sharp, median ridge, which disappears near the center of the 

 platform. Lateral and central muscular scars well developed. 



Type, Lingulasma Schueherti, Ulrich. Hudson River group 

 (Lower Silurian). 



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