IIACTRA.— Plate I. 



The Venus-shaped Mactea. Shell orbicularly subtri- 

 angular, inflated, nearly convex, heart-shaped, nearly 

 equilateral, anteriorly obtuse, posteriorly angled, 

 transversely regularly striated, smooth at the um- 

 boes, dirty-white or grey, posteriorly violet-tinged 

 within and without ; umboes swollen, prominent, ob- 

 liquely cordate ; lunule and area broad, ovate, regu- 

 larly plaited ; sinus of the mantle broad, subserai- 

 circular. 



Deshayes, Pro. Zool. Soc. 1854. 



Huh. China Sea and Japan. 



A tumid heart-shaped species, approaching to the form 

 of GnatJiodon. 



Species 3. (Mus. Cuming.) 



Mactea qdadrangularis. Mact. testa ovato-suhqua- 

 drangulari, tenui, tumidd, cordiformi, suiceguilaterali, 

 transversim plicato-Uratd, squalide grised, epidermide 

 fiavescente tenuissimd iiidutd, latere autlco sul/truncato, 

 lata, posticum subaquaute ; umbonibus tumidis, oblique 

 cordatis, approximatis ; lunula aredque mdistinctis, 

 eleganter pUcatis ; sinu pallli brevi, subtrigono, apice 

 obtuso. 



The qhadeangular Mactea. Shell ovately subqua- 

 drangular, thin, swollen, heart-shaped, nearly equi- 

 lateral, transversely plicately ridged, dirty-grey, co- 

 vered with a very thin yellowish epidermis, anterior 

 side slightly truncated, broad, nearly equal to the 

 posterior; umboes swollen, obliquely cordate, ap- 

 proximated; lunule and area indistinct, elegantly 



plicated; sinus of the mantle short, subtriangular, 



obtuse at the top. 

 Deshayes, Pro. Zool. Soc. 1854. 

 nab. China. 



A thin Cardiuin-]ike species, neatly ridged across, ex- 

 cept in the vicinity of the umboes, which are smooth. 



Species 4. (Mus. Brit.) 



Mactka maxima. Mact. testa perampliter inflatd, ovato- 

 subrhombed, inaquilaterali, transwrsim striata et ru- 

 gosd, albidd, epidermide nigro-fuscd marginem versus 

 indutdy anlice anguste liiante, postice latissinie Idante ; 

 umbonibus magnis, obtusis, approximatis; sinu pallii 

 lata, profunda, horizontali. 



The veey laege Mactea. Shell very largely inflated, 

 ovately subrhomboidal, inequilateral, transversely 

 striated and rough, whitish, covered towards the 

 margin with a black-brown epidermis, anteriorly 

 narrowly gaping, posteriorly very broadly gaping; 

 umboes large, obtuse, approximated ; sinus of the 

 mantle broad, deep, horizontal. 



Lutraria maxima, Middendorf, Malac. zool. Russ. part 3. 

 pi. 66. pi. 19. f. 1-4. 

 Lutraria inflata, Dunker. 

 Tresus maximus. Gray. 



Hab. California. 



This fine species, the largest of the genus, is chiefly re- 

 markable for the wide gaping of its posterior end, which 

 gives to the shell a Panopaa-Yikt form. 



