60 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



LUTRARIA, Lamarck. 



Testa sequivalvis, insequilateralis, transversa, oblonga vel ovata, late- 

 ribus hians. Cardo dentibus alterius valvse duobus ; alterius tri- 

 bus, quorum posticus tenuis, compressus. Dentes laterales nulli. 

 Ligamentum internum, in foveis dentibus adjectis insertum. Im- 

 pressio muscularis pallii sinu magno. 



• 



The shell of Lutraria differs materially from that of Mactra, with 

 which genus the Lutrarise were formerly united. It may be easily di- 

 stinguished by the absence of lateral teeth ; it has also a large sinus in 

 the muscular impression, and may be described as being equivalve, ine- 

 quilateral, transverse, oblong or ovate, and gaping at the sides. The 

 hinge has two teeth in one valve and three in the other, the posterior 

 one being thin and compressed. The ligament is internal, inserted in a 

 pit near the teeth in each valve, and the palleal impression exhibits a 

 large sinus. 



Examples. 

 PI. XLI. Fig. 1. 



Lutraria solenoides, Lamarck, Anim. sans vert., new edit., vol. vi. 



p. 90. 

 My a oblonga, Gmelin. 

 Mactra hians, Montague. 

 Lutricola solenoides, De Blainville. 



PI. XLI. Fig. 2. 



Lutraria papyracea, Lamarck, Anim. sans vert., new edit., vol. vi. 



p. 93. 

 Mactra papyracea, Gmelin. 



