FAMILY 3. AVICULACEA. 145 



linear, and crenulated along the margin ; the crenulse being set in a row 

 so as to form a series of distinct concavities, each containing a portion of 

 the ligament. The muscular impression is of an oblong form, but rather 

 indistinct. It has not yet been satisfactorily ascertained whether the 

 Crenatula? have any byssus ; there is no visible sinus for the passage of 

 it near the hinge, as in the shell of Perna ; so, if it exists at all, we may 

 conclude that it passes out at the ventral margin as in the case of the 

 Pinna. 



Examples. 

 PI. CV. Fig. I and 3. 



Crenatula avicularis, Lamarck, Anim. sans vert., new edit., vol. vii. 

 p. 71. De Blainville, Manuel de Malacologie, pi. 63. f. 2. 



Ostrea semiaurita, Linnaeus. 



PI. CV. Fig. 2. 



Crenatula mytiloides, Lamarck, Anim. sans vert., new edit,, vol. vii. 



p. 73. Annales du Mus., pi. 2. f. 3 and 4. 

 Pinna picta ? Forskael. 



PERNA, Lamarck. 



Testa planulata, fibro-laminaris, subsequivalvis, subirregularis, umbonibus 

 parvis, subfequalibus. Cardo latus, marginalis, sulcis plurimis paral- 

 lelis in utraque valva liratim incisus ; liris non insertis, sulcis liga- 

 mentum divisum inter se excipientibus. Lacuna specialis pro bysso 

 infra cardinis extremitatem posticam ; parietibus incrassatis, aetate 

 crescentibus. Impressio muscularis obliqua, distincte imbuta. 



Linnaeus and his followers included the animals which come under 

 our present consideration among the Ostrea. Lamarck appears to have 

 been the first to separate them in the formation of the genus Perna ; 



vol. i. u 



