KONGL. SV. VET. AKADEMIKNS HANDLINGAU. BAND 26. N:o 2. 13 



noticed this s[)efies in deposits from WarMeiuiiiide in Gerinaiiy uiul from the eastern Smajand 

 in Sweden. 



The microseopical examination of the prae- and inter-gUicial (U-posits of northern (iermany 

 and Denmark have furnished evidence that tliese .strata were formed in inlets from the North Sea 

 and not from the Arctic Sea. 



All these facts prove of what importance the study of fossil diatomacea' is becoming to 

 Greologists. 



Amphiprora Khb. (1848). 



Valve lanceolate, acute, convex. Axial part of the valve elevated into a sigmoid keel, usually 

 separated from the lower part by a line of junction. Axial area indistinct. Central area small 

 or none. Structure of the lower part of the valve: transverse strise, rarely scattered puncta; 

 structure of the keel: puncta in transverse or decussating rows. — Frustule strongly constricted 

 in the middle. Junction between the keel and the lower part of the valve usually visible as a 

 more or less sinuose line. Connecting zone complex, with more or less numerous, transversely 

 striate divisions. — Cell-contents (of A. alata) a single chromotophore-plate along the zone. The 

 division of the chromotophore begins from its ends (Pfitzer, Ban u. Entw. p. 94). 



The name Amphiprora was given by EhrExXBERG 1843 (Am. p. 122) to two naviculoid dia- 

 toms. ^4. con^fricta, the figure of which represents some species of Navicula in the fru.stular view, 

 is slightly constricted in the middle. It seems impossible now to make out what form this name 

 may denote. The other Amphiprora is, as the figures in the Microgeology* shews, A^ar. *S'ew«e«. In 

 the »Bacillarien» Kutzing adds a third species, A. alata, which is distinguished by its sigmoid me- 

 dian line, and the lines on both sides of the median line, as well as by a complex connecting zone. 

 Later on several other forms were described ass Amphiprora by Bailey, W. Smith, and others. 

 W. Smith describes as Ampliiprora ritrca a form with straight median line and not complex con- 

 necting zone. Forms of very heterogenous nature were thus thrown together in the genus Amphi- 

 prora. Rabexhorst tried 18(54, (Fl. Eur. Alg. p. 257) to separate the forms with a sigmoid median 

 line as a new genus, Amphicam2)a, which name Pfitzer 1871 (Bau und Entw. p. 04) changed to 

 AiH2)hitropis. — 1 consider that the name Amphiprora may be retained for the forms with sigmoid 

 keel and complex zone, as A. alata is the tirst recognizable form described. For the other forms 

 I have 1891 (Diatomiste I, p. 51) proposed the name Tropidoneis. 



The genus Amphiprora seems to be akin to the Nitzschiese, and is on the other hand con- 

 nected with Auricula. The complex zone, the single chromatophore, the puncta or lines on the keel 

 remind one of the Nitzschieje. In most species of Amphiprora the keel forms a well marked part of 

 the valve, bordered by a junction-line, which is frequently denticulated or sinuose, and very sug- 

 gestive of the alee of Surirelhe. Whetiier this line projects into a true wing, I have not been 

 able to discover. h\ all cases it occupies the same position as the wing of Surirellse. 



The structure of the valve is somewhat different in different sections. Three types may be 

 distinguished: the type of A. alata, of A. (j'ujatdca, and of A. Ttmpcrei. In the first named the 

 keel as well as the valve have trajisverse strite. In larger forms of that type the stria? seem to 

 be finely transversely lineate, with rather coarser puncta on the keel, which puncta appear to be- 

 long to an interior stratum. In the forms, of which A. ijigantea is the type, the keel and the 

 lower part of the valve have entirely different structure. The keel has puncta, disposed in obli(|uely 

 decussating rows as in Pleurosigma, and the lower part of the valve has transverse stria'. In 

 A. Tenipert'i the keel has two rows of large stigmas and in addition very fine transverse striae, 

 while the lower part of the valve shews only fine scattered puncta. 



Some few forms of Amphiprora live in fresh water, the greater part in brackish water, and 

 some are purely marine. They occur in all parts of the world. 



