CONCHOLOGY. 



Bivalve? 



XLVII. 



My rims. 



Edulis, 



Ungulatus 



Incurvatus 



Pellucidus. 



VTodiohi!, 



tngosus, 



recisus, 



sliape and form than those of the preceding. The Bri- 

 tish species divide themselves into two genera, Mytilus 

 and Pinna. 



Genus XLVII. Mytilus. 



Shell with a hinge marked by a. longitudinal furrow ; 

 hectic towards the shortest end; usually affixed by means 

 of a byssus. 



1. Edulis. Shell oblong, somewhat pointed at the 

 beak, sides sloped ; anterior side a little angulated ; pos- 

 terior side rather indented; inside blue about the mar- 

 gin, whitish in the middle ; teeth like crenulations be- 

 neath the beak ; length three inches, breadth an inch 

 and a half. 



Brit. Shells, tab. 128. fig. 1. 1. 



Brit. Zoo!, tab. 63. fig. 73. 

 Found in vast beds, fixed by the byssus. The com- 

 mon Mussel. 



2. Ungulatus. Shell smooth, somewhat curved ; pos- 

 terior margin inflected, hinge terminal, bidentated; 

 length four or five inches. 



Brit. Shells, tab. 128. fig. 2.2. 

 Found on the coast of Cornwall by Miss Pocock, and 

 on Gullon Links, near Haddington. 



3. Incurvatus. Shell resembling M. edulis, but 

 ' broader in proportion to its length ; posterior side much 



incurvated ; length an inch and a half, breadth an inch. 

 Brit. Zoo/, tab. 64. fig. 74. 

 Inhabits crevices of rocks on the shore, and the roots 

 of alga-. We have taken half a dozen of specimens 

 from the root of one fucus, all of them similar in form, 

 though differing in size. This occurrence supports the 

 opinion, that it is distinct from M. edulis. 



4. Pellucidus. Shell thin, pellucid, of a whitish co- 

 lour, tinged with blue, more or less radiated with 

 deep blue, covered with a yellow epidermis; crenula- 

 tions beneath the beak small ; length about two inches, 

 breadth one inch. 



Brit. Zoo/, tab. 63. fig. 75. 

 Brit. Shells, tab. 81. 

 Frequent on the British shores. 



5. Modiolus. Shell oblong, sub-oval ; posterior side 

 towards the beak extends outwards a little; umbo large 

 and prominent ; length six inches, breadth three inches. 



Brit. Zoot. tab. 66. fig. 77. 

 Brit. Shells, tab. 23. 

 A variety occurs with a deep depression under the 

 beak, and which has been termed M. umbilicatus. The 

 young of the shell is known by the name of M. barba/us. 

 Like the common Mussel, this species is abundant, and 

 is gregarious. It is considered as an excellent bait for 

 the haddock. In Zetland it is called Yogue. 



6. Rugosus. Shell oblong, sub-oval, with rugged con- 

 centric wrinkles ; side next the hinge always rounded, 

 the opposite side sometimes truncated; umbo small, 

 placed near to one end ; it usually gapes at one end, 

 and opposite to the hinge ; length an inch and a quar- 

 ter, breadth about half its length. 



Brit. Zool. tab. 63. fig. 72. 

 Brit. Shells, tab. 141. 

 Found burrowed in limestone, and in the roots of fuci. 



7. Pr, cisus. Shell oblong, irregular, rugose ; hinge 

 close to one end of the shell, which is truncated ; beak 

 large and prominent, projecting more in one valve than 

 m the other; length a quarter of an inch, breadth half 

 an inch. 



Test. Brit. tab. 4. fig. 2. 



99 



Bivalves. 

 Crista-ealfi. 



Disco: 



Not uncommon among the roots of fuci. 



8. Crista-galli. Shell rude, rugged, compressed, va- 

 rying much in shape, colour, opake, ferruginous ; mar- 

 gin scolloped, or cut into deep irregular notches in 

 both valves, corresponding and mutually inserted ; dia- 

 meter two inches and a half. 



Chimn. Conch, tab. 75. fig. 683. 



Mr Montagu states, that it is found adhering to the 

 bottoms of ships. 



9- Discors. Shell convex, sub-cordated, pellucid; 

 the posterior and anterior sides ribbed; the middle area 

 plain, or faintly wrinkled transversely; umbo large, 

 prominent, apex much turned to one side; margin cre- 

 nated on the part where striated ; length three eighths, 

 breadth half an inch. 



Brit. Shells, tab. 25. 

 Frequent on the English coast, adhering to the Asci~ 

 dia mcntula. In Scotland, where it is common, it is 

 principally found among the roots of Fucus digilatus 

 and Polyscides. 



10. JDiscrepans. Shell sub-oval, compressed, pellu- Discre'j.ins 

 cid, covered with a black epidermis ; both sides round- 

 ed, the anterior one largest, divided into three com- 

 partments, like the preceding species; sometimes an 

 inch and a half in breadth. 



Test. Brit. tab. 26. fig. 4. 

 Found in Wales and Devonshire by Mr Montagu. 

 Not uncommon in the Frith of Forth. 



11. Cygneits. Shell thin, fragile, semi-pellucid, oval, Cygneus, 

 wrinkled concentrically, and covered with an olivaceous 

 green epidermis ; umbo very small, placed nearest one 

 end ; inside glossy, pearlaceous ; length two inches and 

 a half, breadth nearly six inches. 



Brit. Zool. tab. 67. fig. 78. 

 Brit. Shells, tab. 55. 

 Found in England in ponds and stagnant waters. 



12. Anatinus. Shell thin, semi-pellucid, oval, of a Anatinus, 

 greener colour than the last, less convex, and the mar- 

 gin at the hinge more prominent, rising into a sort of 

 angulated wing ; length two inches, breadth three in- 

 ches and a half. 



Brit. Zool. tab. 68. fig. 79. 

 Brit. Shells, tab. 113. 

 Frequent in rivers in England and Scotland. 



13. Avonensis. Shell suboval, olivaceous, with con- Avonensis, 

 centric wrinkles ; size of the preceding, but broader in 

 proportion to its length, and not so much produced at 

 the hinge ; posterior side more obtuse ; front margin 

 nearly straight, or frequently subarcuated. 



Lin. Trans, vol. viii. tab. 3. A. fig. 4. 

 Found by Mr Montagu in the River Avon, about 

 Lackham in Wiltshire. 



14. Plicalus. Shell oblong, truncated on one side, Plicatus, 

 close to the umbo ; thin, pellucid, uneven, slightly pli- 

 cated, beaks small, incurvated, and placed at one end, 

 the opposite end broadest ; inside glossy ; length half 

 an inch, breadth one inch. 



Chimn. Conch, tab. 82. fig. 733. a. b. 



Found alive off the Isle of Sky by Mr Laskey. 



lo.Decussatus. Shell longitudinally ovate, sides equal, Decussatiis, 

 finely striated longitudinally, crossed by more minute 

 stria: in a transverse direction, giving it a decussated 

 appearance, when examined under a microscope ; in- 

 side smooth, nacred; near the front margin a reflected 

 transverse ridge ; length one eighth of an inch, breadth 

 not so much. 



Test. Brit. p. 69. Sup. 



Found by Mr Laskey in sand near Dunbar. 



