328 



Mytilus hamiltonensis, Tate. 



1887. Mytilus hamiltonensis, Tate, Trans. Roy. Soc. South Aust. vol. ix. 

 p. 186, pi. xviii. fig. 9. 



Distinguislied by its external ornament, consisting of very 

 numerous, frequently bifurcating, radial threads, crossed by closely- 

 set striae of growth ; the inner margin of the valves is denticulated 

 all round ; and there are two or three small teeth under the umbo 

 in the right valve. 



The author compares it with the living M. hirsutus, Lamarck. 



Dimensions. — Height 56 mm. ; length 27-5 mm. 



Form, and Loo. — Miocene : Muddy Creek, Yictoria. 



L. 4823. Specimen of the gerontic stage of growth. 



Presented hy John Dennant, Esq. 



L. 9833. Two examples of the adult. Purchased. 



Genus SEPTIFER, Eecluz. 



[Eev. Zool. 1848, p. 275.] 



Ventral border concave or sinuous for the passage of the byssus ; 

 surface of the valves radiately striated ; umbones slightly inflected, 

 having in the interior a thin plate on which is the impression 

 of the anterior adductor of the valves ; the cardinal border has 

 a few dentiform crenulations. 



Type. — Mytilus lilocularis, Linnaeus. 



Septifer fenestratus, Tate. 



1886. Septifer fenestratus, Tate, Trans. Roy. Soc. South Aust. vol. viii. 



p. 124, pi. ix. fig. 1. 



1887. Septfer fenestratus, Tate, id. vol. ix. p. 187. 

 1889. Septifer fenestratus, Dennant, id. vol. xi. p. 49. 



Shell elongate, much flattened on one side; surface ornament 

 consisting of closely-set, divaricate lineations, much broken up 

 by the platy ridges of growth ; internal plate small, sinuous at 

 the edge ; margin of the valves closely crenulated inside, dentate 

 under the umbo ; byssal sinus small. 



