88 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



2. Subgen. Amygdalum, Megerle (1811). 



Shell compressed, surface smooth, shining, periostracum polished, 

 not hirsute. Type, M. pictus, Lam. (= arborescens, Chem.). 



Modietta, Monterosato, is said by Dall to be a synonym. Not only 

 M. lut-eus, Fischer, but also M. politus, Verrill, and other deep-sea 

 species spin a nest like Lima. 



3. Subgen. Gregariella, Monterosato (1884). 



Surface decussate, with central smooth area ; shell tumid, periostra- 

 cum hirsute. Type, M. Petagnee, Scacchi. Botulina, Dall, is a synonym. 



Dall appears to me to be right in placing this form in the genus 

 Modiolus, instead of Modiolaria, as Fischer has done. I observe that 

 in Mytilus Podriguezi, Orb., the radial striae are also obsolete in the 

 central part of the shell. 



4. Subgen. Brachydontes, Swainson (1840). 



Surface radially sulcate. Type, M. demissus, Dillwyn ( = plicatulus, 

 Lam.). 



M. demissus, on account of its marginal umbones, is a true 

 Modiolus, having besides its edentulous ■ hinge. The dentigerous 

 species with subterminal beaks I have united with Hormomya. 



5. Subgen. Botula, Morch (1853). 



Surface deeply, concentrically sulcate ; shell inflated, with 

 conspicuously spiral umbones ; periostracum polished. Type, 

 M. cimiamomeus, Lam. 



SPECIES OF MYTILUS AND MODIOLUS, INHABITING THE 

 EASTERN COASTS OF SOUTH AMERICA. 



Genus MYTILUS, Linn. 



Subgen. ETJMYTILTJS, Jhr. 



1. Mytilus edulis, Linn. 



Mytilus edulis, Linnaeus : Syst. nat., 10th ed. (1758), p. 705 ; 12th ed. 



(1766), p. 1157. 

 ,, Platensis, Orbigny : Voy. Anier. merid., torn, v [1846], p. 645, 



pi. lxxxv, figs. 3, 4. 

 ,, Patagonicus, Orbigny : t.c, p. 646, pi. lxxxv, figs. 12, 13. 

 ,, Platensis, Orb.: Hidalgo, Mol. Viaje Pacifico, pt. ii (1869), 



p. 53, pi. iii, fig. 5. 

 ,, Fischerianus, Tapparone-Canefri: Zool. Viag. Magenta, Malac. 



(1874), p. 138, or Mem. Accad. Sci. Torino, ser. n, 



torn, xxviii (1876), p. 242, pi. iv, fig. 1. 

 ,, edulis, Linn. : E. A. Smith, Phil. Trans., vol. clxviii (1879), 



p. 189. 



