946 SUMMARY OF CURRENT RESEARCHES RELATING TO 



in the marking. In the European slides I have generally found 

 them coarser than in gatherings from warmer seas, but they differ a 

 good deal in the same place. The shell is made up of segments 

 radiating from the large granulated umbilicus, and these segments are 

 marked as if cut from sheets of perforated silex, and bent into place 

 on the convex surface of the valve, the edges of the segments often 

 showing lines of apiculi obscuring the suture. In the coarser speci- 

 mens the areolae are but little more difficult to define than in Odont. 

 suhtilis, and in broken ones the fracture may be unmistakably traced 

 through the punctae. The colour test shows also the same appearances 

 as in the species last described. From this we may follow the in- 

 creasing fineness of the marking till the dots run together into a 

 diagonal striation rivalling the Pleurosigmas, and approaching 

 (though with a considerable interval) that of Hyalodiscus suhtilis. 



As far as we can succeed in defining small areas and minute 

 irregularities of fractured edges, we find the hexagons diminishing to 

 dots and these to still finer punctsB, but they continue to have all the 

 characteristics of an arrangement of areolee between two laminee. It 

 is fair to conclude that in those specimens of Podosira maculata in 

 which we cannot define the areolae, they nevertheless exist, and we 

 might add that it is at least probable that the same structure would 

 be found in Hyalodiscus suhtilis if our glasses were more powerful. I 

 intend to continue for the moment, however, within the region of 

 observation, and to postpone drawing conclusions till we have 

 examined a greater number of species. 



The Actinocyclus, in its different varieties, is a very interesting 

 genus to study in connection with the preceding series. It is found 

 with disks of less than '001 in. in diameter, and running up to the 

 splendid proportions of A. Halfsii, measuring sometimes over '008 

 in. In some of the smaller species the dots are comparatively large, 

 and the disk will be found subdivided by six or more radial lines 

 of areolge, each line containing only six or eight of the large 

 dots. In the larger kinds the rays are often fifty or more, with as 

 many areolae to the radial line. The segments are filled, of course, 

 with similar areolae, arranged upon a series of parallel lines. I think 

 I may say that of all the species and varieties of this disk which I 

 have examined, there is none of which I have not found examples of 

 separated laminae, showing inner and outer plates as in Coscinodiscus, 

 none in which the line of fracture does not prove the dots in both 

 plates to be the weak places. Some of the smaller disks with large 

 areolae are found in gatherings from the Samoa Islands and other 

 places in the Indian Ocean. MoUer's slides from the Baltic at Kiel 

 give a large range of sizes and conditions. A preparation oSA.fuscus 

 {Cos. fuscus Norman) from Yarra Yarra, Australia, made by Wheeler, 

 shows an unusual number of separated laminae, an examination of 

 which will confirm my assertion. The fossil earths of Nottingham 

 and Calvert Co., Maryland, are full of Actinocyclus, and the deposits of 

 Santa Monica and San Luis Obispo, on the Pacific coast, are rich in 

 various forms of the same genus, with great range in the size of the 

 punctse. 



