LAMELLIBRANCHIATA. 79 



Tlie contour changes from the ol)Hquely cordiform or quite triangular (see PI. Ill, fig. gi; just 

 as in C. rxiguum) to become broadly oval or almost circular. 



There is also great variation in regard to the sculpture. Sometimes for example, the ribs may 

 be rough with scales and pointed tubercles not only on the anterior and posterior area, but the 

 middle area may also be partially or wholly beset with scales or tubercles; in this way we obtain a 

 form such as that figmcd in I'l. Ill, fig. 9c, the sculpture of which resembles thai in C. iindnsuiii, but 

 transitions show, that it can be traced back to the common form C.fasciahnii with smooth, central 

 ribs. In the young, with contour like that of C. exigutiiii^ the posterior ribs arc beset with very 

 ]5ointed and comparatively long spines. 



The ribs are usually quite flat and only separated by a fine line, but ven,' often the interspace 

 between them is somewhat broader, yet never so broad as the ribs themselves. Sometimes, however, 

 the ribs are more or less convex, especially when they are separated b\- a distinct interspace. Not 

 rarely an intercostal sculpture is seen under the lens in the form of a fine pricking (PL III, fig. 9k). 



I have further represented (PI. Ill, fig. 9f, g and h) that form of C.fasciatuvi , which was con- 

 fused by Morch with C.rdiile; the resemblance is striking, indeed, but the pointed tubercles on the 

 posterior ribs (PL III, fig. 911) reveal its true nature — in C.cdiiie the rugosities are lamelliform here. 



Cardium nodosum Turton. 

 [Faeroes], 

 To this species Morch (Vidensk. Medd. Naturh. Foren. Kbhvn. 1867, p. 94) refers 7 specimens 

 from Thorsha\-n in the Fteroes. I have not been able to find these specimens here in the Museum, 

 and as the species is not present in the considerable collections, which have been made at the Fteroes 

 in recent years, I think it vcr\' doubtful, if the species occurs there. Possibh-, an unusually well 

 sculptured form of C.fasciatuiii (cf. above and PL III, fig. 9e) has given rise to the confusion. 



Cardium ciliatum Fabricius. 



PL III, fig. 10 (young). 



Cardium ciliatitiii Fabricius, Fauna groenl., 1780, p. 410. — Cardiitii/ islaudicitiii Chemnitz, Conch. 



Cab. VI, 17S2, p. 200, PL 19, fig. 195 — 96. ') -- Cardiuui puhfscois Co u th o u y, Boston Journ. Nat. 



Hist. II, 1838, p. 60, PL 3, fig. 6 — Cardium arcticuiii Sowerby, Proc. Zool. Soc. 1840, p. 106; 



Conch. Illustr., 1841, fig. 26. — C«;7//>//// //(7j)r.f// St im pson, Proc. Acad. Nat. Sc. Philadelphia, 



1863, p. 58; Packard, Mem. Boston Soc. Nat. Hist. I, 1867, p. 278, PL 7, fig. 14. — Cardium 



islandicum Gould & Binney, Rep. Invert. Mass., 1870, p. 139, fig. 450. — Cardium ciliatuin 



Sars, MolL Reg. Arct. Norv., 1878, p. 46, PL 5, fig. 4. 

 Cardium cdulc Mohr (non Linne), Forsog til en Island.sk Naturhistorie, 1786, p. 128. — Cardium 



islandicum Moller, Index MolL GroenL, 1842, p. 20. — Cardium ciliafuiu Morch, Rink's 



the material collected from Denmark; it is onlj- among the specimens from the Kattegat that there are some which resemble 

 the ventricose, keeled form from Iceland and the Faeroes. 



I) Chemnitz is the autlior of the name Carduiin islandicum, not Linne, as the species first occurs in the 13th Ed. 

 of Syst. Nat, pars 6, 1792 (p. 3252) and with a reference to Chemnitz' work of 17S2. By erroneously referring the name 

 C. islatidicum to the 12th Ed. (1767) of Linnei Syst. Nat. (though no Cardium of that name occurs there), several older authors 

 have got the present species renamed "Cardium islaiidimm Linne"; this error appears again in Kobelt's Prodr. Faun. Moll. 

 Test. Mar. Eur. (1880). 



