8 P. T. CLEVE, NOTES ON SOME ATLANTIC PLANKTON-ORGANISMS. 



Diameter of the outer shell 0,i, of the interiör 0,04, of the meslies 0,oi millim. 

 Very rare at 45° N. 49° W. (1899 January). Temperatur? 12. Salinity 35,54. 

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

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



Haliomina irregulare. N. Sp. 

 Plate V. Fig. 4. 



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

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

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

 1 'i »res 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,ot, of the meshes 0,oi to 

 0,03 millim. 



Very rare at 45° N. 49° W. (January 1899). Temperature 12. Salinity 35,54. 



Haliomma spinulosum var.*) 

 Plate V. Fig. 7. 



I have met with specimens having two concentric, exteriör shells with very wide 

 irregular meshes and thread-like bars. The interiör 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 there före be classified 

 as Echinomuia. It seems as were the number of exteriör shells variable, and it may be 

 possible that Arachnosphcera comprises forms with an increased number of shells, espe- 

 cially as the interiör shell of Haliomina spinulosum is similar to those of Arachnosphoera 

 myriacantha and A. oligacantha. 



Heliospha^ra minuta <^r- 

 Plate 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 pyraniidal, few, IV2 times as long as the radius. 

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



Diameter 0,05 to 0,ot; pores 0,oot;; bars 0,noc, main-spines 0,02 to 0,of> millini. 



Rare at 41° N. 21°— 23° W., 49° N. 18° W., 62° N. 11° W. (March 1898) and 1 7° N. 

 71° W. (August 1898). Temperature 11,7, mean of 4 observations, max. 14,9, min. 8, 

 exeeptionally 27,2. Salinity 35,63, mean of 3 obs., max. 35, st, min. 35,37. 



*) The same form has been figured by J0KGENSEN (Bergens Museums Aarbog 1 s;»'.>, X. 6, 1'1. III, iig. 18) 

 as Arachno8ph&ra dichotoma. 



