KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. N:0 2. 91 



45. D. chersoneusis Grun. (1875). — V. panduriform, usiially slender, with sitbelliptical 

 segments. L. 0, 055 to. 0, 15; B. 0, 02 to 0,o6; at the constr. 0, 012 to U,o.3 mm. Central nodule with 

 parallel, appi-oximate horns. Furrows very narrow, linear. Träns verse costse 8 to 13 in 0, 01 mm., 

 crossed by 2 to 5, not imdnlating, almost straight longitudinal costtB. — Nav. cherson. Grun. A. S. 

 Atl. XII f. 40, LXIX f. 21. Nar Apis. A. S. N. D. Pl. I f. 9. Atl. XII f. 18 to 23, 25. 



Marine: North Sea! Mediterranean Sea! Zanzibar (Atl.), Ceylon! Philippines! China! Tahiti! 

 Galapagos Islands! West Indies! Florida! Cape Horn (Petit). Fossil: S:ta Monica Calif. 



This very widely distributed species is nsually regarded as Nav. Apis of Ehrenberö. I am 

 unable to make out what this name, as is the case with so many others of the names given by 

 Ehrenberg, may denote. Nav. Apis of Donkin (B. D. p. 48 Pl. VII f. 3) and of Schmidt (Atl. XII 

 f. 16; LXIX f. 41, 43, 44) are nnknoAvn to me. Specimens from England in the coUection of Grove 

 are identical with D. incurvata. D. chersonensis is nearly akin to D. splencUda, intermediate forms 

 being freqnent. Such a form is the fig. 24 Pl. XII in A. S. Atl. and Nav splendiäa var. arata 

 A. S. (Atl. XIII f. 13, 14, 16, 33, 35). To D. chersonensis belongs most likely Nav Hantkenii 

 Pant. (II p. 46 Pl. VIII f. 150). On corroded specimens the longitudinal costa? are less distinct 

 and the transverse more or less fragmentary. Such corroded specimens form Brnns Nav. pedalis 

 (D. esp. nouvelles p. 36 Pl. XVI f. 10; 1891. A. S. Atl. CLXXIV f. 14, 15; 1892), original speci- 

 mens of which I had an opportunity of examining. 



46. D. Weissflogii A. S. (1873). — V. strongly constricted, with subelliptical segments. 

 L. 0,0.33 to 0,11; B. 0.014 to 0,035; at the constr. 0,oo9 to 0, 025 mm. Central nodule with ap- 

 proximate horns. Furrows not distinct from the other rows of alveoli. Transverse costffi 7 to 8 

 in 0,01 mm., crossed by numeroiis equidistant, straight, longitudinal costa;, curved outwards in the 

 middle of the valve. On the middle of the valve the costEe are slightly divergent and not, or 

 only close to the central nodule, crossed by longitudinal costfB. — Nav. Weissflogii A. S. Zeitschr. 

 f. ges. Natur. 1873 p. 406 Pl. VI f. 3, 4. A. S. Atl. XII f. 26 to 32. V. H. Syn. p. 90 Svxppl. B. 

 f. 21. Nav. diversa Grev. Ed. N. Ph. J. XVIII p. 186 f. 14; 1863.? 



Marine: Bab el mandeb! Madagascar! Ceylon! Singapore! Philippines! Samoa! Tahiti! Sand- 

 wich Islands (Atl.), Gulf of Mexico! Florida! North Carolina! 



47. D. areolata Cl. N. Sp. — V. moderately constricted, with subelliptical segments. 

 L. 0,1.3; B. 0,045; at the constr. 0, 028 mm. Central nodule large, its horns almost parallel. Furrows 

 linear, with strongly marked transverse costse.. Transverse costse 4, in 0, 01 mm., crossed by a 

 few, slightly curved longitudinal costifi, 3 in 0, 01 mm., which are interrupted in the middle of the 

 valve. The rectangular areolfe, formed by the two sets of costiE are large and have in their middle 

 one or two ocelli. — Pl. I f. 28. 



Marine: S:ta Monica, Calif., fossil (Deby Coll.)! 



48. D. domblittensis Grun. (1882). — V. elliptical. L. 0,027 to 0,045; B. 0,oi5 to 0,022 

 mm. Central nodule large, quadrate. Furrows narrow, of equal breadth the whole length. Trans- 

 verse costse 10 in 0,oi mm. anastomosing and thus prodncing more or less regular longitudinal 

 rows of elongated alveoli, about 7 in 0, 01 mm. No fine punctation visible. — Nav. e.cpleta v. donib. 

 Grun. Foss. D. Öster. Ung p. 156 Pl. XXX f. 60. Nav. hilarula Pant. III Pl. XV f. 230 (1893). 

 Dipl. domb. leon. n. Pl. II f. 2. 



Fresh or slightly brackish water: Sweden, Lefrasjön in Skåne! Mälaren! Domblitton, foss.! 

 Gulf of Bothnia! Common in the Baltic deposits of the Ancylus-epoch ! 



This form seems to be closely connected with D. didyma, of which it may be a non-con- 

 stricted freshwater form. Grunow consideres it as connected with D. notahilis. 



