KONGL. fSV. VKT. AKADEMIEN8 HANDLINGAR. BAND 26. N:0 2. 91 



45. 1). chersonensis (Iiun. {1H75). — V. paiKluriform, usually slender, with suhelliptical 

 segments. L. 0,05.^) to 0, i."); B. 0,o2 to 0,06; at the constr. 0,012 to 0,0.3 mm. Central nodule with 

 parallel, approximate horns. Furrows very narrow, linear. Transverse costn- H to 13 in 0,01 mm., 

 ci'ossed hy 2 to 5, not uiululating, almost straight longitudinal costa;. — Nav. rhcrson. (tHi n. A. 8. 

 Atl. Xll f. 40, LXIX f. 21. Nav Airis. A. S. N. J). PI. I f. !). Atl. Xll f. 1« 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 C'alif. 



This very widely distributed sj)ecies is usually regarded as Nav. Apis of Eiirenbeik;. 1 am 

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

 Ehrenber(4, may denote. Nav. Apis of Donkin (B. D. p. 48 PL VII f. 3) and of Schmidt (Atl. XII 

 f. Ki; LXIX f. 41, 43, 44) are unknown to me. Specimens from England in the collection of Grove 

 are identical with D. incurvata. D. chersonensis is nearly akin to I), splendida, intermediate forms 

 being frequent. Such a form is the fig. 24 PI. XII in A. S. Atl. and Nav splendidu var. ((rata 

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

 Pant. (II p. 46 PI. VIII f. 150). On corroded specimens the longitudinal costte are less distinct 

 and the transverse more or less fragmentary. Such corroded specimens form Bi'uns Nav. pjcdalis 

 (D. esp. nouvelles p. 36 PI. XVI f. 10; 1«91. A. S. Atl. CLXXIV f. 14, 15; 1892), original .siieci- 

 mens of which I had an opportunity of examining. 



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

 L. 0,033 to 0, n; B. 0.oi4 to 0,o35; at the constr. 0,oo9 to 0,o2 5 mm. Central nodule with ap- 

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

 in 0,0 1 mm., crossed by numerous equidistant, straight, longitudinal costa;, curved outwards in the 

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

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

 f. ges. Natur. 1873 p. 406 PI. VI f. 3, 4. A. S. Atl. XII f. 26 to 32. V. H. Syn. p. 90 Suppl. 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.), (xulf of Mexico! Florida! North Carolina! 



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

 L. 0,13; B. 0,04 5; at the constr. 0,o2 8 mm. Central nodule large, its horns almost parallel. Furrows 

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

 few, slightly curved longitudinal costa;, 3 in 0,oi mm., which are interrupted in the middle of the 

 valve. The rectangular areola;, formed by the two sets of costa; are large and have in their middle 

 one or two ocelli. — PI. I f. 28. 



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



48. D. (lomblittensis Gruin. (1882). — V. elliptical. L. 0,027 to o.o-i.i; B. 0,015 to 0,022 

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

 verse costpe 10 in 0,oi mm. anastomo.sing and thus producing more or less regular longitudinal 

 rows of elongated alveoli, about 7 in 0,oi mm. No fine punctation visible. — Nav. expleta v. dontb. 

 Grun. Foss. D. Oster. Ung p. 156 PI. XXX f. 60. Nav. Mlarula Pant. Ill PI. XV f. 230 (1893). 

 DijiJ. donih. Icon. n. PL II f. 2. 



Fresh or slightly brackish water: Sweden, Ijefrasjon in Skane! Malaren! Domblitton, foss.! 

 (xulf of Bothnia! (!ommon 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 I). notahUis. 



