MYTILUS. 171 



309. — Index Testaceolog. pi. 12, f. 2-3. — Mawe, Con- 

 ch ology, pi. 16, f. 2. 

 l\f)/tiliis incurvatus, PviNN. Brit. Zool. ed. 4, vol. iv. p. Ill, pi. 64, f. 74. — 

 Mont. Test. Brit. p. 160.— Mat. and Rack. Linn. Trans, 

 vol. viii. p. 105, pi. 3, f. 7. — Laskey, Mem. Wern. Soc. 

 vol. i. p. 391. — TuRT, Conch. Diction, p. 109; Dithyra 

 Brit. p. 197.— Index Testaceolog, pi. 12, f. 4«. 

 „ vulgaris. Da Costa, Brit. Conch, p. 216, pi. 15. f. 5 (on the left). 

 Perna migulma, Retzius, Nov. Test. Genera, p. 21, 

 Mi/tilusflavus, PoLi, Test. Sicil. vol, ii. p. 207, pi, 32, f. 4. 



„ sagitlatus, PoLi, Test. Sicil. vol. ii. p. 208, pi. 32, f. 2, 3. 



„ yalloproviticialis, Lamarck, Anim. s. Vert. (ed. Desh.) vol. vii. p. 46. 



— Philippi, Moll. Sicil. vol. i. p. 72, pi. 5, f. 12, 



13 ; vol. ii. p. 53, — Hanl, Recent Shells, vol. i. p. 



249. 



„ albrevialus, Lamarck, Anim. s. Vert, (ed, Desh.) vol. vii. p. 47. — 



PoTiEZ and Mich. Galerie Douai, vol. ii. pi. 54, f. 1, 

 „ reiusus, Lamarck, Anim. s. Vert, (ed, Desh.) vol. vii. p. 48, 

 „ liesperianusj Lamarck, Anim. s. Vert. (ed. Desh.) vol. vii. p. 48 (pro- 

 bably).— Payraud. Cat. Moll. Corse, p. 68, pi. 2, f. 5 

 (probably). 

 „ dilatatus. Gray, 'Annals Philos. 1825; Index Testaceol, Suppl, pi, 2, 



Mytil. f. 2. 

 „ subsaxatiUs, Williamson, Mag. Nat. Hist. vol. vii. p. 353. — Couch, 

 Cornish Fauna, pt. 2, p. 34, — Brit, Marine Conch, p, 109. 



The extreme variation of contour to which this species is 

 hahle, has caused its varieties to be designated by several 

 appellations. Certain characters, however, pervade them 

 all, among which the absence of true teeth may be regarded 

 as one of the most essential importance. 



That which we regard as the typical form, meaning 

 thereby the shape which is naturally assumed by a species 

 not forced to adapt its proportions to the circumstance of 

 its habitat, is not what we are accustomed to view it in the 

 stalls -of the fishmongers, narrow and subarcuated, but 

 rather the dilated and triangular subsaxatiUs, whose soli- 

 tary haunts permit a freer development of its several parts, 

 than the gregarious habits of the more frequent variety 

 allow of. In this, then, the form is shorter and subtrigonal, 



