konCtL. sv. vet. akademiens handlingak. band 27. N:0 3. 111 



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

 connected, that I am iinable, after comparison of a large number of sketebes, to group tbem in 

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

 ends, changes mucb according to its position. Tbe ventral side, wbicb in larger specimens has a 

 row of short costate strite, has in some forms a few strite at tbe ends only and in otbers none at 

 all. Tbe double rows of puncta alternating witb tbe costse are in some specimens not distinct. 

 Smaller forms are closely connected witb Ä. crassa var. spuria. 



6. A. tesselata Grove and Stdrt (1887). — V. linear, witb inwards cnrved, obtiise ends. 

 L. 0,io; B. 0,0 IS mm. Median line biarcuate. Dorsal side witb strong, smootb transverse costte, 

 5,5 in 0,0 1 mm. crossed by longitudinal costse, about 7 in 0,oi mm. Ventral side witb coarse, 

 costate striaj. — Q. M. Cl. III (2) p. 131 Pl. X f . 1. 



Marine: Oamaru, N. Zealand, fossil! 



Tbis peculiar form seems to me certainly to belong to tbe gro^^p of A. crassa, bnt differs 

 from all otber forms by its peculiar structure. Tbe dorsal side of tbe valve seems to be covered 

 witb quadrate alveoli, disposed in transverse and longitudinal rows. Tbe specimens I have seen were 

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

 means of very oblique ligbt in seeing on tbe ventral side, a row of strong, costate stria; and on 

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

 crossed by transverse costate strise. 



7. A. inelegans Cl. and G-rovb (1891). — V. sublunate, witb incurved, obtuse ends. L. 0,o9; 

 B. 0,03 mm. Median line biarcuate. Axial and central areas indistinct on tbe dorsal and ventral 

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

 Ventral side without central area and witb strong, costate strise, divergent, between tbe central 

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



Marine: Macassar Straits! 



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

 B. 0,0 15 mm. Median line biarcuate. Dorsal side witb strong, smootb, costate strise, 6 in 0,oi 

 mm., reacbing to the median line and crossed by a narrow, blank line. Ventral side witb ronnded 

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



Marine: Java! 



This form is very dissimilar to tbe type, but it is difficult to find any specifically distinct 

 characteristic. 



8. A. orn.ita Leud. Fortm. (1879). — V. linear, witb incurved, obtuse ends. L. 0,i; B. 0,02 

 mm. Dorsal side witb 8 costate strise in 0,oi mm. crossed by a linear furrow and reacbing to tbe 

 median line. Ventral side witb 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 CoU.)! 



I have seen a single valve only, tbe opaque strvicture of which did not ad mit of a close 

 examination of tbe dorsal side. Still there can be no doubt tbat tbis form is a distinct species, 

 belonging to the group of A. crassa. 



9. A. comorensis Cl. N. sp. — V. broadly linear, witb obliquely rounded and sligbtly 

 incurved ends. L. 0,i4 to 0,i9; B. 0,O2 5 mm. Median line strongly biarcuate andelevated. Dorsal side 

 witb transverse rows (7 in 0,oi mm.) of large pnncta (10 in 0,oi mm.) not reacbing to tbe median 

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



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



Tbis is a large and distinct form, akin to A. ornata. Tbe opaque structui^e and the eleva- 

 tion to a keel of tbe median line made tbe examination of the dorsal side difficult. Still 1 believe 

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



