1884.] 



MICEOSCOPICAL JOURNAL. 



87 



specimens of Podosira Alaculata 

 {^Hyalodiscus Stelliger^ Bailey) , and 

 these will be found of very varying 

 degrees of fineness 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 obscur- 

 ing the suture. In the coarser speci- 

 mens the areolae are but little more dif- 

 ficult to define than in Odont. Subtilis^ 

 and in broken ones the fracture may 

 be unmistakably traced through the 

 punctcB. The color test shows also 

 the same appearances as in the species 

 last described. From this we may 

 follow the increasing fineness of the 

 marking till the dots run together into 

 a diagonal striation rivalling the Pleu- 

 rosig?nas^ and approaching (though 

 with a considerable intei^val) that of 

 Uyalodiscus SubtUis. 



As far as we can succeed in defining 

 small areas and minute irregularities 

 of fractured edges, we find the hexa- 

 gons diminishing to dots and these to 

 still finer punctae, but they continue 

 to have all the characteristics of an 

 arrangement of areolae between two 

 laminse. . It is fair to conclude that in 

 those specimens of Podosira macu- 

 lata in which w^e cannot define the 

 areolae, they nevertheless exist ; and 

 we might add that it is at least prob- 

 ble that the same structure would be 

 found in Uyalodiscus Subtilis if our 

 glasses w^ere more powerful. I in- 

 tend to continue for the moment, 

 however, within the region of observ- 

 ation, and to postpone drawing con- 

 clusions 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 pre- 

 ceding series. It is found with discs 

 of less than .001 inch in diameter, and 



running up to the splendid propor- 

 tions of A. Ralfsii^ measuring some- 

 times over .008 inch. In some of the 

 smaller species the dots are compara- 

 tively large, and the disc will be found 

 subdivided by six or more radial lines 

 of areolae, 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 areolse, ar- 

 ranged upon a series of parallel lines. 

 I think I may say that of all the spe- 

 cies and varieties of this disc which I 

 have examined, there is none of which 

 I have not found examples of sepa- 

 rated lamina, showing inner and outer 

 plates as in Coscinodiscus^ and none 

 in which the line of fracture does not 

 prove the dots in both plates to be the 

 weak places. Some of the smaller 

 discs with large areolae are found in 

 gatherings from the Samoa Islands 

 and other places in the Indian Ocean. 

 Moller's slides from the Baltic at Kiel 

 give a large range of sizes and condi- 

 tions. A preparation of A. fuscus 

 {^Cos. ftiscus^ Norman) from Yarra 

 Yarra, Australia, made by Wheeler, 

 shows an unusual number of separa- 

 ted lamiuEe, an examination of which 

 will confirm my assertion. The fos- 

 sil earths of Nottingham and Calvert 

 Co., Maryland, are full of Actinocy- 

 clus^ and the deposits of Santa Mo- 

 nica 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 punct^e. 



There is a tendency in most of the 

 species to accumulate silex upon the 

 spaces between the areolfe, giving a 

 roughened and irregularly granulated 

 appearance to the outer surface of the 

 disc. This condition also interferes 

 with a satisfactory examination of the 

 ' dots' by causing iiTegular refraction, 

 &c. For this reason we need to se- 

 lect smooth and evenly-marked speci- 

 mens for one part of the investigation, 

 though for another the roughened ex- 

 amples are most instructive. We find 

 this thickened coating broken away 



