KONfil.. 8V. VET. AKADEMIENS PIANDLINGAR. BAND 27. N:0 3. Ill 



This species is very variable and comprises a number of forms, which however are so closely 

 connected, that I am unable, after comparison of a large number of sketches, to group them in 

 separate species or varieties. Besides, the form, and appearance of the valve, especially of the 

 ends, changes much according to its position. The ventral side, which in larger specimens has a 

 row of short costate strise, has in some forms a few strise at the ends only and in others none at 

 all. The double rows of puncta alternating with the costee are in some specimens not distinct. 

 Smaller forms are closely connected with A. crassa var. spuria. 



6. A. tesselata Gkove and Stuet (1887). — V. linear, with inwards curved, obtuse ends. 

 L. 0,io; B. 0,015 mm. Median line biarcuate. Dorsal side with strong, smooth transverse costse, 

 5,5 in 0,01 mm. crossed by longitudinal costge, about 7 in 0,oi mm. Ventral side with coarse, 

 costate striae. — Q. M. CI. Ill (2) p. 131 PL X f. 1. 



Marine: Oamaru, N. Zealand, fossil! 



This peculiar form seems to me certainly to belong to the group of A. crassa, but differs 

 from all other forms by its peculiar structure. The dorsal side of the valve seems to be covered 

 with quadrate alveoli, disposed in transverse and longitudinal rows. The specimens I have seen were 

 mounted in a position, not favourable for examination of the ventral side. Still I succedeed by 

 means of very oblique light in seeing on the ventral side, a row of strong, costate strise and on 

 the dorsal side not far from the median line a longitudinal line, the space between the lines being 

 crossed by transverse costate striae. 



7. A. inelegans Cl. and Grove (1891). — V. sublunate, with incurved, obtuse ends. L. 0,o9; 

 B. 0,0 3 mm. Median line biarcuate. Axial and central areas indistinct on the dorsal and ventral 

 side. Dorsal side with 7 costate striae in 0,oi mm. crossed by a narrow, blank longitudinal line. 

 Ventral side without central area and with strong, costate striaj, divergent, between the central 

 nodule and the ends, towards the median line. — Diatomiste I p. 68 PI. X f. 15. 



Marine: Macassar Straits! 



Var.? polita Cl. — V. stout, elongated, with broad, obtuse and incurved ends. L. 0,o6; 

 B. 0,015 mm. Median line biarcuate. Dorsal side with strong, smooth, costate strise, 6 in 0,oi 

 mm., reaching to the median line and crossed by a narrow, blank line. Ventral side with rounded 

 central area and strong, costate striae, crossed by a narrow, blank line. — PL IV f. 40. 



Marine: Java! 



This form is very dissimilar to the type, but it is dilEcult to iind any specifically distinct 

 characteristic. 



8. A. ornata Lbud. Fortm. (1879). — V. linear, with incurved, obtuse ends. L. 0,i; B. 0,o2 

 mm. Dorsal side with 8 costate striae in 0,o i mm. crossed by a linear furrow and reaching to the 

 median line. Ventral side with inclined rows (7 in 0,oi mm.) of puncta, crossed by a longitudinal, 

 narrow area. — D. de Ceylon p. 20 PL I f. 9. 



Marine: Ceylon (Le Tourneur Coll.)! 



I have seen a single valve only, the opaque structure of which did not admit of a close 

 examination of the dorsal side. Still there can be no doubt that this form is a distinct species, 

 belonging to the group of A. crassa. 



9. A. comorensis Cl. N. sp. — V. broadly linear, with obliquely rounded and slightly 

 incurved ends. L. 0,i4 to 0,i9; B. 0,025 mm. Median line strongly biarcuate and elevated. Dorsal side 

 with transverse rows (7 in 0,oi mm.) of large puncta (10 in 0,oi mm.) not reaching to the median 

 line. Ventral side with curved rows of large and distant puncta, crossed by a narrow blank area. 



Marine: Nossibe (Brun Coll.)! Tamatave (Kinker Coll.)! 



This is a large and distinct form, akin to A. ornata. The opaque structure and the eleva- 

 tion to a keel of the median line made the examination of the dorsal side difficult. Still I believe 

 that the dorsal rows of puncta are crossed by a keel or longitudinal line. 



