8 p. T. CLEVE, NOTES ON SOME ATLANTIC PLANKToN-OROANlSMS. 



Diameter of the outer shell 0,i, of the interior U,04, of the meshes 0,oi millira. 

 \'ory rare at 45 N. 49 W. (1899 January). Temperature 12. Salinity 35,54. 

 Similar to H. mditoinma, but smaller, with thicker bars and smaller meshes. The 

 thickness of the cortical shell prevented all examination of the medullary shell. 



Halioinma irregulare. N. Sp. 



Plate V. Fig. 4. 



Pores of the cortical shell irregular, rounded, of different size and forrn. Spines 

 stouter main-spines and smaller by-spines, the former Vo of the radius. By-spines scat- 

 tered at intervals. Cortical shell thin-walled, 3 times as broad as the medullary shell. 

 Poi-es irregular rounded, 3 to 9 times as broad as the bars. Medullary shell with rounded, 

 smaller pores. 



Diameter of the outer shell 0,22, of the medullary shell 0,07, of the meshes 0,oi to 

 0,03 millim. 



Very rare at 45 N. 49 W. (January 1899). Temperature 12. Salinity 35,r,4. 



Halioinma spinulosuin var. *) 



I'late V. Fig. 7. 



I have met with specimens having tuio concentric, exterior shells with very wide 

 irregular meshes and thread-like bars. The interior shell had, as usually, very regular 

 hexagonal meshes. There is thus no other difference between this form and the normal, 

 than that the variety has three, in stead of two, shells and should therefore be classified 

 as Echinomma. It seems as were the number of exterior shells variable, and it may be 

 possible that Arachnosjjha'ra comprises forms with an increased number of shells, espe- 

 cially as the interior shell of Haliornma spinulosiim is similar to those of Arachnosphara 

 iiiyriacantha and A. oligacantha. 



Heliosphfpra minuta Cr.. 

 riato VI. Fig. 2. 



Thick-walled, 5 to 6 times as broad as the meshes. Pores regular, all equal, hexa- 

 gonally framed- Main-spines three sided pyramidal, few, l',2 times as long as the radius. 

 By-spines short, acute, arising from the nodal points of the meshes. 



Diameter 0,05 to 0,0?; pores 0,ooii; bars 0,oo6, main-spines 0,o2 to 0,ob millim. 



Rare at 41 N. 21 23^W., 49^ N. 18 W., 62 N. 11W. (March 1898) and 17 N. 

 71 W. (August 1898). Temperature 11,7, mean of 4 observations, max. 14,y, min. 8, 

 exceptionally 27,2. Salinity 35,63, mean of 3 obs., max. 35, s7, min. 35,37. 



*) The same form has licen tignrcd hy Jorgensen (Borgens Museums Aarbog 1899, N. (!, PI. Ill, fig. 18) 

 as Araclmospha'ra dichotoma. 



