110 Transactions of the Society. 



Dijflugia oblonga Ehrenb. may be taken as a type of the tests 

 in this group ; it is more or less pear-shaped with a circular 

 aperture at the smaller end, the outlines are as regular as the 

 selection of fairly evenly-sized sand-grains will permit, the inner 

 surface is smooth and the interior is nearly entirely occupied by 

 the animal. 



The tests of many species of Ditflugia have pockets forming 

 horn-like extensions ; these may vary in number from a single 

 terminal one to a dozen, as in D. corona Wallich, and these horns 

 are occasionally terminated by a sharp splinter or grain of sand. 

 They are, when normal in number, placed symmetrically on the 

 test, but additional ones are apt to be inserted unevenly, as in 

 D. bicornis Penard (PI. II, figs. 1, 2). 



A very common material used to form tests consists of diatom 

 frustules ; a few species such as I). bacilli/era Penard and D. bacil- 

 lariarum Perty (PI. II, figs. 3,4), employ them almost exclusively ; 

 many others intermix them with other materials. 



The tests in this group have usually circular apertures, occasion- 

 ally they are elliptical, and several species have lobed or crenulated 

 openings with a marked tendency to variation in the number of 

 lobes. Thus, in Dijflugia gramen Penard and D. lobostoma Leidy, 

 three or four is the normal number, but five or six are not rare ; 

 D. oviformis Cash has three to five, and D. corona Wallich twelve 

 to twenty. In connexion with this kind of aperture it is curious 

 that in Europe the Arccllm rarely depart from the circular form 

 of aperture, whilst in North America the crenulated form frequently 

 occurs in several species. 



The genus Pontigulasia presents us with a different type of 

 aperture ; the test proper is more or less oviform and similar in 

 material and appearance to that of a Dijjlugia, but over the small 

 end, which has one or more openings, is fixed a short conical tube 

 contracted at the line of junction, the outer end forming the visible 

 aperture. The orifice or orifices of the test proper are therefore pro- 

 vided with a small vestibule or anti-chamber. Pontigulasia brgophila 

 Penard has a single circular inner orifice ; P. spiralis Khumbler 

 has two such ; P. incisa Ehumbler and P. compressa (Carter) Cash 

 have two also, but formed by a narrow bridge-piece placed across 

 a circular opening ; P. vas (Leidy) Schouteden has a single inner 

 orifice placed eccentrically, and usually a second one opposite which 

 is closed or covered over by a translucent diaphragm. The junction 

 of the buccal tube with the body of the test is very frequently 

 strengthened by some large quartz-grains, cemented around it at 

 equal distances apart. 



The tests of the genus Lesquereusia are similar except that their 

 form is spheroidal and the outer tube is affixed tangentially ; in 

 some instances it is so short as to merge into the general outlines 

 of the test, and in L. mimetica Penard (6') does so completely. 



