456 Bulletin American Museum of Natural History [Vol. LII1. 
Driessenids in which there is a recurved myophore for the pedal retractor muscle 
accessory to the septum within the beaks. Externally the shell is without radial 
sculpture. 
This genus occurs in estuaries of eastern North America, Africa, 
and, according to Dall, China and the Viti Islands. It was abundant in 
the European Miocene. . 
The thin-shelled, recent forms are referable to the subgenus 
Mytilopsis Conrad. 3 : 
The species of this group have often been referred to Driessena 
(“‘ Dreissensia’’),+ but they differ from that genus by possessing a separate 
myophore for the pedal retractor muscle, accessory to the septum, and 
directed toward the cavity of the valve. It is often scarcely seen in a 
direct. view, but is conspicuous in an oblique view into the cavity (Fig. 
94b). 
The following species have been described from Africa: 
Congeria africana (P. J. Van Beneden) = Dreissena africana P. J. VAN BENEDEN, 
1835 (April), Ann. Sc. Nat. Zool., (2) III, p. 211, Pl. vu, figs. 12 and 18. Upper 
Senegal. The author also describes the animal. 
Mytilus cochleatus ‘‘Kickx’”’? Nysr (1835, Bull. Ac. Sci. Belgique, IT, p. 235, PL., 
figs. 1-3; séance du 4 juillet), described from specimens found alive at Antwerp, 
where they may have been introduced from Africa, has been regarded by some authors 
as a synonym of C. africana, but the published drawings of the two forms are very 
different. 
Congeria cyanea (P. J. Van Beneden) = Dreissena cyanea P. J. VAN BENEDEN, 
1837, Bull. Ac. Sci. Belgique, IV, p. 41, Pl., figs. 1-5. Presumably from Senegal; 
exact locality unknown. 
Congeria gibberosa (Preston) = Dreissensia gibberosa Preston, 1909, Ann. Mag. 
Nat. Hist., (8) IV, p. 89, Pl. tv, fig. 4. Assinie, Ivory Coast. 
Congeria holmi (A. d’Ailly) = Dreissensia holmi A. dD’ A1tuy, 1896, Bihang Svenska 
Vet. Ak. Handl., XXII, Afd. 4, No. 2, p. 180, Pl. v, figs. 17-23. Ekumbi, Cameroon. 
Congeria lacustris (Morelet) =Dreissena lacustris Moreumt, 1860, Journ. de 
Conchyl., VIII, p. 191. Dreissensia lacustris MORELET, 1885, op. cit., XX XIII, p. 
p. 32, Pl. 11, fig. 11. Lake Ebrié, Grand Bassam, Ivory Coast. 
Congeria ornata (Morelet). See p. 457. 
; 1In the first notice of this genus by P. J. Van Beneden (1885, Bull. Ac. Sci. Belgique, II, p. 25; 
séance du 17 janvier) the name is spelled Driessena, and the specimens discussed were said to have been 
received from M. Driessens. Thegenus was then monotypic for Mytilus polymorphus Pallas. Subse- 
quently in the report of the meeting of the Belgian Academy of February 7 (1835, II, p. 44), Dumortier 
mentions Van Beneden’s memoir as “Histoire naturelle et anatomique du Dreissena polymorpha.’ 
In the index of the same volume, p. iii, the name appears as Dreissenia. In the memoir published in 1835 
(April), Ann. Sc. Nat. Zool., (2) III, p. 193, Van Beneden uses the form Dreissena. 
P. Oppenheim (1891, Zeitschr. Deutsch. Geol. Ges., XLIII, p. 927) states that the name of the man 
whomit wastheintentiontohonor was Dreyssens,sothat thecorrect orthography would be Dreyssensia. 
He gave (pp. 932-934) a catalogue of recent and fossil species now included in Driessena and Congeria. 
Dall (1898, Trans. Wagner Free Inst. Sci. Philadelphia, III; p. 808) prefers the form Dreissensia. 
_ As there appears to be no way of reconciling the several versions of the name, we preferto use the 
ones form, ee : 
e genus Mytilina Cantraine (1837, Ann. Sc. Nat. Zool., (2) VII, p. 306) included M. pol 
(Pallas), type of Driessena, and M. cochleata “ Kickx,’’ a species of oo M. eee 
‘ selected as type. Cantraine apparently had intended to call the genus Mytilomya, as he used the form 
Mytilomyes”’ in his discussion under Mytilina. Bronn (1838, ‘Lethea Geognostica,’ II, p. 921) 
latinized the name as ‘‘ Mytilomya Cantraine.’’ This name will take th 1 
Pas a e the same species M. polymorpha 
