84 PROCEEDINGS OF THE MALACOLOGICAL SOCIETT. 



ON THE SOUTII AMERICAN SPECIES OF MYTILID.E. 



By H. von Jhering. 



Read 9th March, 1900. 



In studying the Mytilidse of Brazil and Patagonia, and their relation- 

 ships with allied species in other parts of the globe, some facts 

 appeared singular, more especially the want of precision in distinction 

 between certain groups of Mytilus and Modiolus, and the association of 

 Mytilus cdulis with species belonging to quite a different section. 



To Dr. W. H. Dall, in his excellent work on the Tertiary Fauna 

 of Florida (Trans. "Wagner Free Inst. Philadelphia, vol. iv, pt. 4, 

 1898), we owe a new treatment of the divisions and subdivisions of 

 the Mytilidse. So far as the separation of Mytilus and Modiolus is 

 concerned, Dall accepts the old views, separating the two by the 

 position of the umbones and the presence or absence of teeth. Neither 

 of these characters is decisive, and there are forms, as, for example, 

 Modiolus citrinus, Bolten (= sulcatus, Lam.), in which the teeth are 

 much more developed than in many species of Mytilus. The 6ame is 

 true of the position of the umbones. These are terminal in Mytilus 

 eduks, Linn., and allied forms, non-terminal in many species of 

 Modiolus ; on the other hand, there are species of Mytilus with non- 

 terminal umbones, and of Modiolus with terminal beaks. In Modiolus 

 Trailli, Eve., the umbones are terminal, and in M. capax, Conr., nearly 

 so._ These forms offer no difficulty in their classification with the 

 allied species of Modiolus, but there are others in which this is not 

 the case. _ There are a great number of species, both of Mytilus and 

 Modiolus, in which the umbones are more or less terminal, and situated 

 above the anterior extremity of the shell. This is the case in 

 Mytili belonging to the group of M. Solisianus, Orb., M. minimus, Poli, 

 etc., and also in the sections Rormomya, of Mytilus, and Bracliydontes, 

 of Modiolus. In these subgenera the umbones offer no reason for 

 generic separation, nor does the dentition. Comparing Modiolus 

 citrinus, Bolt., with Mytilus Doming ensis, Lam., the position of the 

 umbones is the same in both, but the teeth are more developed in the 

 former species, which is also more solid. Really it would be more 

 natural to completely change the generic position of both. Clessin, 

 m hi^ monograph of the Mytilidge (Martini & Chemnitz, Conch.-Cab., 

 vol. viii, pt. 3, 1889), figures both species under the name of Modiola 

 sulcata, Lam. Of the figures, pi. iv, fig. 10, and pi. xxv, figs. 5, 6, 

 really refer to this species, but pi. xxxi, figs. 9, 10, represent Mytilus 

 Domingensis, Lain., a species which he also described (p. 87, pi. xxv, 

 figs. 1, 2) as Mytilus Orbignyanus, Clessin. Mytilus oralis, Lam., 

 offers another instructive example. This species is figured by Clessin 

 (pi. xxxiii, figs. 4, 5) as Modiolus ovalis, Clessin, and what he describes 



