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



45. p. chersonensis Geun. (1875). — V. panduriform, usually slender, with subelliptical 

 segments. L. 0,055 to 0,i5; B. 0,o2 to 0,o6; at the constr. 0,oi2 to 0,o3 mm. Central nodule with 

 parallel, approximate horns. Furrows very narrow, linear. Transverse costse 8 to 13 in 0,oi mm., 

 crossed by 2 to 5, not undulating, almost straight longitudinal costee. — Nav. cherson. Geun. A. S. 

 Atl. XII f. 40, LXIX f. 21. Nav 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 usually regarded as Nav. Apis of Ehkenberg. 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 PI. VII f. 3) and of Schmidt (Atl. XII 

 f. 16; 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 D. splendida, intermediate forms 

 being frequent. Such a form is the fig. 24 PL XII in A. S. Atl. and Nav splendida var. arata 

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

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

 and the transverse more or less fragmentary. Such corroded specimens form Bruns 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. 0,033 to 0,ii; 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 costee 7 to 8 

 in 0,01 mm., crossed by numerous equidistant, straight, longitudinal costse, curved outwards in the 

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

 only close to the central nodule, crossed by longitudinal costse. — 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 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.), Gulf of Mexico! Florida! North Carolina! 



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

 L. 0,13; 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,oi mm., crossed by a 

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

 valve. The rectangular areolse, formed by the two sets of costse 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 producing more or less regular longitudinal 

 rows of elongated alveoli, about 7 in 0,oi mm. No fine punctation visible. — Nav. expletav. domb. 

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

 Bipl. domb. Icon. n. PL II f. 2. 



Fresh or slightly brackish water: Sweden, Lefrasjon in Skane! Malaren! 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. notaiilis. 



