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MONOGRAPH OF THE GENUS 



LINGULA, Brvg. 

 By G. B. Sowerby, F.L.S., etc. 



Char. Gen. Testa tenuis, subsequivalvis, ajquilaterahs, ovato- 

 elongata, depressa, apice subtruncato, basi subacute pediculo 

 affixa. Impressioues musculares in utraque valva quatuor, ad 

 utrumque latus duse, altera basalis, altera subcentralis. 



Shell thin, consisting for the most part of a horny epidermis, 

 bned with a small quantity of calcareous matter within ; its gene- 

 ral form when the valves are closed is an elongated oval, com- 

 pressed and much resembling a duck's bill, (whence the specific 

 appellation of the first known species). The two valves are very 

 nearly equal, the dorsal being somewhat thicker and more acumi- 

 nated at the base. When in a state of rest, the two valves are 

 closed at the edges in all parts. There is neither ligament nor 

 hinge, the two valves being held together by the adductor muscles. 

 Muscular impressions several in each valve, arranged in pairs, one 

 pair nearly central, another toward the posterior part, and a third, 

 small and double, close to the posterior apex. The shell is attached 

 by a peduncle which is fixed within the apex of the dorsal valve. 



Of recent species seven are here described and figured, more 

 than double that number are known iu a fossil state, as charac- 

 terizing the various secondary and tertiary deposites. 



DESCRIPTIONS. 



1. Lingula anatina (pi. lxvii. f. 1, 2, 3, 9, 10.) Lam. 



L. testa oblonga, compressa, longitudinaliter substriata, apicis 

 basisque valvarum latitudinc sequali, apice subtrilobo, valva, ven- 

 trali medio intus longitudinaliter incrassata. 



Shell oblong, compressed, slightly striated longitudinally, equal 



