BIVALVIA. 59 



Dreissena Brardii, Faujas St. Fond. Tab. XII, fig. 3, a — e. 



Moule. Fauj. St. Fond. Ann. du Mus., t. viii, t. 58, tigs. 11, 12. 



Mytilus Brardh. Brongn. Terr. calc. Trap, du Vincentin, t. 6, fig. 14, 1823. 



— — Gold/. Petr. Germ., vol. ii, p. 2/1, t. 129, fig. 10. 



— — J. Sowerby. Min. Conch., t. 532, fig. 2, 1826. 



— — Bronn. Leth. Geog., t. ii, p. 923, pi. 39, fig. 10, 1836. 



— — Nyst. Rech. Coq. foss. Hoess. et Kl. spaw., p. 13, No. 22, 1836. 

 ? — — var. $ 1 Basterot. Bordeaux Foss., No. 2, p. 78. 



1 — Basteeotii. Dujardin. Tr. Geol. Soc. Fr., vol ii, p. 269. 



? — acutirostris. Gold/. Petr. Germ., t. v, pi. 129, fig. 11, p. 272. 



? SPATHULATUS. Id. - - fig. 12. 



Congeria Basteroti? Desk. Conch., 650, t. 37, figs. 15, 16. 

 Dreissena Brardii. Morris. Catal. Brit. Foss., p. 202, 1854. 



— — Pictet. Traite de Palseont., pi. 81, fig. 11. 



— Basteroti. Nyst. Conch. Foss. Belg., p. 265, pi. 20, fig. 7 a — c. 



— Sowerbyi. TtOrbigny. Prod, de Palseont., t. 11, p. 425, No. 1637, 1850. 



Spec. Char. D. testa ovatd vel elongato-cuneatd ; laevigata, obtuse carinatd ; umboni- 

 bus acutis ; septo cochleaio. 



Shell ovate or elongately wedge-shaped, smooth, and obtusely carinated ; beaks sharp 

 and pointed ; septum concave. 



Length, §ths of an inch. 



Localities. Ilordwell, Headon Hill {Forbes). 



Belgium, Limbourg {Nyst), Weisenau, En v. de Mayencc {A.Brongniart). 



This little shell is abundant in the fine sandy stratum at Hordwell which has yielded 

 so many beautiful vertebrate fossils. Upwards of a hundred specimens were obtained by 

 myself, congregated in and around the upper jaw of Alligator Ilantoniensis. It is pos- 

 sible that the decomposition of the flesh of the dead reptile may have rendered the water 

 at that place favorable to the multiplication of the mussel. I found the shell elsewhere, 

 but in no other place in so great abundance. 



My specimens are variable in outline; the proportions in some are from "l\ to 1, while 

 in others they are not more than 1^ to 1, the more elongated being also the more 

 tumid. The umbo is a little inflected, and in some specimens there is a flattening on 

 the siphonal region. The shelf is of a moderate size, and is not entirely occupied by the 

 muscle, the mark of which is indented on it, and is of a roundedly oval shape. The 

 cartilaginous portion of the connexus extended about two fifths of the longest diameter of 

 the shell, and, like that of Mytilus, it was nearly covered by the dorsal edge. Many 

 specimens of a small Serpula {tenuis) were found with this mussel in association with 

 numerous specimens of Limnaeae, Cyrenae, &c, and in one of the specimens there is 

 what appears to be the arenaceous case of a Sabella (fig. 3 a). We have, thus, 

 supposed marine animals living in fresh water with Liinnaese, or we have the supposed 



