LAMELWBRANCHIATA. 



57 



"Idas argenteus is probably the species of that name noticed by Verrill as var. lamellosa" , and the 

 added knowledge of Idas argenteus obtained in that year really disposed of the peculiarities <>f 

 Verr ill's Idas. 



Modiolaria. 



The 4 northern species of this genus may, according to my experience, most readily be dis- 

 tinguished from one another in the following manner: 



The shell 

 radially 

 striated 



over the whole M. faba. 



not distinctly separated M. nigra. 



only on anterior 

 or also on the 

 posterior area. 



Central 

 and poster- 

 ior areas of 

 shell 



separated 

 by a dia- 

 gonal fur- 

 row. 



Central 

 area 



smooth M. discors 



(cum var. laevigata et substriata). 

 shagreen-like wrinkled M.corrupata. 



Modiolaria discors Linne. 

 The true Modiolaria discors Linne does not occur at Greenland, Jan Mayen or Iceland. The 

 species is represented here by "Modiolaria Icevigata Gray" and ■■Modiolaria substriata Gray", which I 

 do not consider separate species, but varieties of a species which also embraces "Modiolaria dis, 

 Linnc". The last name has the prior right by age and must consequently have the advantage in 

 the designation of the species. 



var. laevigata G r a y. 

 PL III, figs. 4a— b. 



Modioli/ laevigata Gray, Parry's first voyage, Suppl. to App., 1824, p. 244. Crcnclla .',, 



Tor ell, Spitsbergens Molluskfauua, 1859, p. 133. — Modiolaria discors Gould X' 

 Biuney, Rep. Invert. Mass., 1870, p. 192, fig. 489. Modiolaria Icevigata Sars, Moll. Reg. 



Arct. Norv., 187S, p. 29, PL 3, fig. 3; Leche, Vega-Exped. Vetensk. Arb. Ill, 1883, p. 450, PI. 34, 

 figs. 27—28. 



Mytilus discors Fabricius, Fauna groenl., 1780, p. 418. -- Mytilus discors, arcticus Fabricius (partim), 

 K. D. Yideusk. Selsk. Skr. 1788, p. 453, figs. 1 X 4—6. - Modiola discors Moller, Index 

 Moll. Groenl. , 1842, p. 19. — Modiolaria discors P.eck, in Gairnard, Voyage de la Recherche, 

 PL 17, fig. 2 a— h. — Modiolaria lev is Beck, ibid. PL 17, fig. 3L - ■ Modioli discors Beck, 

 Amtl. Bericht 24. Versamml. deutsch. Naturf. in Kiel, 1847, p. 115. -■ Modiolaria Icevigata 

 Morch, Rink's Grouland, 1857, p. 94; Vidensk. Medd. Naturh. Foren. 1868, p. 224; Arctic 

 Manual, 1S75, p. 133; Rink's Dan. Greenland, 1877, p. 442; Becher, Osterr. Polarst. Jan 

 Mayen III, 1886, p. 69; Posselt, Medd. om Gronland, XIX, [895, p. 67; ibid. XXIII. [898, 

 p. 25; Jensen, ibid. XXIX, 1909, p. 326. — Modiolaria corrugata (11011 Stimpson) et laevigata 

 Hagg, Ark. for Zoologi, Bd. 2, No. 2, 1904, p. 22 & 23. 



The Ingolf-Expcdition. II , 



