76 



1785. Mytihts discors, Oceani Aiistralis etc. Chemnitz, Conch.-Cab., VIII, p. 195, pi. LXXXVI, 



figs. 768 (i, 2). 

 1790. Mytilus discors Gmelin (non Linn.), Syst. Nat. (éd. XIII), p. 3356. 

 1797. Mytilus Lamatiis Humphrey, Mus. Calonnianum, p. 43. 



1797. Bruguière, Encyclopéd. Méthod., pi. CCIV, figs. 5 <?, b. 

 1817. Mytilus impactus Dillwyn, Descr. Cat., I, p. 320. 



1819. Mytilus discors Lamarck (non Linn.), Anim. sans Vertèb., VI, p. 114. 



1825. Mytilus impactus Wood, Ind. Test., p. 59, pi. XII, fig. 40. 



1836. Modiola discors Deshayes in Lamarck, Anim. sans Vertèb., VII, p. 23. 



1843. Modiola impacta Hanley, Rec. Biv. Shells, p. 241. 



1845. Modiola impacta Catlow & Reeve, Conch. Nomencl., p. 72. 



1857. Modiola impacta Reeve, Conch. Icon., X, Modiola, pi. IX, fig. 64. 



1857. Crenella [Modiolaria) cor Adams, H. & A., Gen. Rec. Moll,, II, p. 515, 



1860. Modiola impacta Reeve, Elem. Conch., II, p. 72. 



1872. Crenella impacta von Martens, Malakozool. Blàtt., XIX, p. 25. 



1873. Crenella discors Hutton (non Linn.), Cat. New Zealand Moll., p. 78. 

 1880. Crenella impacta Hutton, Man. New Zealand Moll., p. 168. 



1884. Modiolaria impacta Tryon, Struct. Syst. Conch., III, p. 264, pi. CXXVIII, fig. 99. 



1889. Modiolaria impacta Clessin in Martini Chemn. Conch.-Cab. (N. F.), VIII (3), Mytilacea, 



p. i47> pl- XXXIV, fig. 9. 



1890. Crenella [Modiolaria) cor and C. (M.) impacta Paetel, Cat. Conch. Samm., III, p, 194. 

 1901. Crenella impacta Suter, Trans. New Zealand Inst., XXXIV, p. 223. 



1904. Modiolaria impacta Pritchard & Gatliff, Proc. Roy. Soc. Victoria, XVII, p. 253. 



1907. Modiolaria impacta Suter, Trans. New Zealand Inst., XXXIX, p. 263. 



191 3. Modiolaria impacta Suter, Man, New Zealand Moll., p. 869. 



191 5. Modiolaria impacta Suter, Man. New Zealand Moll., Plates, pl. LVIII, fig. 7. 



Mîisculus impactus is closely allied to J/. auiiingiamis (Reeve), but the shell of the 

 latter is comparatively much more elongated and not so high or gibbous. The anterior radial 

 ribs of M. wipactus are also much stronger and more granular. I figure a shell froni New Zealand. 



Distribution : — M. impactus has so far been recorded from New Zealand and Australia. 



In the "Siboga" Collection there is a spécimen from the Anchorage between Nusa Besi 

 and the N. E. Point of Timor (St. 282), which I am unable to separate from spécimens of 

 M. impactus from New Zealand. I also refer, with some doubt, a very young shell from St. 282 

 to this species. 



Genus Lithophaga Rôding. 



1798. Lithophaga Roding, Mus. Boltenianum, p. 156. 



181 1. Lithophagus Megerle, Mag. Ges. Naturf. Freunde Berlin, V, p. 69. 



1857. Lithophaga Adams, H. & A., Gen. Rec. Moll., II, p. 518. 



1858. Lithodomus Reeve, Conch. Icon., X, Lithodomus pl. I (explanation). 

 1886. Litliodomus Fischer, P., Man. Conchyliol., p. 969. 



1898. Lithophaga Dali, Trans. Wagner Free Inst. Sci. Philadelphia, III, p. 798. 



The génotype of Lithophaga Rôding is Lithophaga lithophaga (Linn.), but this species 

 is, as most conchologists agrée, a composite one ; the better known of the two types confused 

 by LiNNAEUS is Lithophaga dactylus (Sowerby) and this was suggested as the type of the subgenus 

 Lithophaga s. s., by Dall. 



The second subgenus represented in the "Siboga" collection is Botula Môrch '), with 

 Lithophaga [Botula) cinnamomea (Lamarck) as its type. 



i) Môrch, G. A. L., Cat. Yold^ II, p. 55, (1853). 



