K()N(;L. SV. vet. AKADEMIEXS llAXJ)LlN(iAli. I5AM) 27. N:() 3. 107 



Forma major. — Frnstule in L. 0, i;!:i; B. 0,()ti mm. Strifu 7 in (),(ii mm. — A. Sr/mi. 

 A. S. Atl. XXVIII f. 3. 



Marine: Campeachy Bay (Atl.). 



Forma minor. — Frnstule in L. 0,o7; B. 0,o2.'i mm. Stria*, 12 in 0,0 1 mm. 



Marine: Pensacola! Lal)uan! 



Var. alafa Cl. — As the type, but with a liyaline limbus projecting from tlie doi'sal .side 

 L. 0,o.').5; B. 0,0;!.') to (),04.'> mm. Stria- 10 in 0,0 1 mm. 



Marine: China! Japan (Brun Coll.)! Barbados! Florida! 



Var. Schleinitzil Jan. (1876). — Frustnle in L. 0,i2 to 0,i.',, in B. 0,or,ti mm. Zone without 

 puncta. Dorsal side with a hyaline limbus. The striiu 8 in 0,oi mm. coarsely punctate; puncta 

 7 in 0,0 1 mm. — A. SchleinitsU A. S. Atl. XXXIX f. 9, 10. 



Marine: Gulf of Naples (Deby Coll.)! Samoa (Atl.). 



I am unable to find any specific difference between A. Sclimidtii and A. Schlcinitzii. The 

 structure of the connecting zone is variable. In some specimens I have seen, besides the longitu- 

 dinal rows of large pearls, very fine scattered puncta, giving it a brownish colour. The absence 

 or presence of a limbus seems also not be of any specific value. 



A. Schmidtii is a form of a peculiar type, remarkable for the elevation of the valve to a 

 keel bearing on its siimmit the median line as in Auricula. 



Subgenus Diplamphora Cl. 



Frustule in outline usually elliptical, or rectangular, with rounded, truncate, or rostrate ends, 

 sometimes indented in the middle. Zone with more or less numerous longitudinal divisions, more 

 or less coarsely, transversely, costate or striate. Valve linear to semilanceolate, with obtuse or 

 protracted ends; its dorsal^ side with one (or two) longitudinal lines. Structure: transverse costse 

 or rows of puncta. Ventral side structureless, punctate, or costate, with or without longi- 

 tudinal line. 



This group comprises a number of species, very different in appearance, but agreeing in the 

 complex connecting zone and the longitudinal line on the dorsal side. They are nearest akin to 

 Amphora, vsensu stricto", but differ in the complex zone. Whether this characteristic be of 

 such importance that the two groups are to be regarded as distinct genera, I cannot at present 

 state with certainty. There are among the Amphoree some forms with tendency to a complex 

 zone, for instance A. robusta var. suhplicata and A. Schmidtii. In all cases Amphora and Dipl- 

 amphora are to be considered as allied groups, having in common a more or less distinct longi- 

 tudinal line or keel on the dorsal, and frequently also on the ventral, side of the valve. This 

 characteristic as well as the structixre of the valve point to a relation to the genus Diploneis, 

 although no intermediate forms have hitherto been discovered. 



The species of this subgenus are very variable in size and form, and the valves in many 

 cases present very different appearances according to the position, in which they lie. These cir- 

 cumstances make the distinction of species and the construction of an artificial key extreme- 

 ly difl^cult. All forms of this group are marine and occur in all seas, but in the gi-eatest 

 variety in the tropical. Many of them are foi;nd in a fossil state in Hungary, Japan and New- 

 Zealand. 



Artificial key. 



^ J Frustle indented in the middle 2. 



■ 1 - not - " — 9. 



) Central nodule stauroid 3. 



^- \ ~ -not - 7. 



) Axial area broad r A. exsecta Grun. 



1 — — narrow or indistinct i. 



