DREISSENA. 165 



D. POLYMORPHA, PallllS. 



Plate XLII. fig. 4, 5, and (Animal) plate Q, fig. 4. 



Mytilus polymorphus, Pallas, It. Russ. vol. i. p. 478. — Schroter, Einleit. 

 Conch, vol. hi. p. 471. — Gmelin, Syst. Nat. p. 33G3. — 

 J. Sowerbv, Trans. Linn. Soc. vol. xiv. p. 585 ; 

 Zoolog. Journ. vol. i. p. 584. — Ferussac, Bull. Sciences 

 Nat. 1826, p. 142. — Index Testaceolog. Suppl. pi. 2, 

 Mytilus, f. 6. — Sowerby, Genera of Shells, Mytilus, 

 f. 4. — Deshayes, Lam. Anim. s. Vert. (ed. Desh.) vol. 

 vii. p. 50. — Reeve, Conch. Systemat. vol. i. pi. 102, 

 f. 4.— Hani.. Recent Shells, vol. i. p. 250, Suppl. pi. 2, 

 Myt. f. 6. 

 Mytilus efluvio Volga, Chemn. Conch. Cab. vol. xi. p. 256, pi. 205, f. 2028. 

 „ ? Volffensis, Gray, Annals Philosoph. 1825, p. 139. 

 „ lineatus, Haardenburg, Commentatio de H. N. Molluscorum Belgi- 



corum (fide de Haan, Van Beneden, <xc.) 

 „ ttageni, Baer, ad instaurat. solemnium adjecta Mytili novi descriptio 

 (Koeningsb. 1825) ; Oken's Isis, 1826, pt. 5, p. 525 (fide 

 Van Beneden). 

 „ Area, Kickx, Desc. nouv. espece de Moule. 1834. 

 Dreissena polymorphs,, Van Beneden, Annales de Sc. Nat. 1835, p. 210, pi. 8, 

 f. 1 to 11.— Strickland, Mag. Nat. H. 1838, p. 361. 

 —Gray, Manual L. and F. W. Shells, p. 300. — Brown, 

 Illust. Conch. G. B. p. 76, pi. 20, f. 4 to 9. 

 Tichogonia Chemnitzii, Rossmassl. Iconog. Land and Siissw. Moll. p. 113, pi. 3, 

 f. 69. 



There is no fear of this naturalized bivalve being con- 

 founded with any other shell at present discovered in our 

 Islands. Its peculiar painting separates it from any 

 species to which it is the least allied in form. This 

 painting consists of chocolate-coloured flexuous or zigzag 

 markings, arranged in a concentric direction upon a white 

 ground, which are chiefly displayed in the younger indi- 

 viduals, and towards the beaks of the elder examples, and 

 usually become more scanty in number, and less beautifully 

 undulating, as they approach the hinder termination, and 

 are entirely absent, in every stage of growth, from the 



