CALF- AND PILSBRY — ON PYRGULOPSIS. II 



angled, well rounded before; peritreme continuous, almost riraate, 

 closely appressed to parietal wall. 



Operculum light corneous, spiral, closely fitting the aperture. 



The following account and illustration of the dentition is by Mr. 

 Charles E. Beecher, who has devoted much attention to the dentition 

 of this group : 



"Jaw thin, membranaceous. 



"Odontophore .62'"'" in length, and . I5 mm in width. There are usu- 

 ally fifty-five transverse rows of teeth, arranged according to the for- 

 mula 3 — 1 — 3, which is common to the family Rissoidce. 



"Rhachis distinct, occupying one-fourth the width of the ribbon. 

 Rhachidian tooth (Fig. 1) short and broad, with the infero-lateral angles 

 produced and slightly arcuate. On each side of the anterior face is a 

 strong, short, conical process or basal tooth projecting outward and 

 somewhat downward. Basal margin trilobate; central lobe truncate. 

 Cusp curved forward, and extended into a strong denticle with four 

 smaller ones on each side. The formula of the denticles for this tooth 

 would, therefore, be : 



4 + 1 + 4 



1 + 1 



"Body of intermediate tooth* subrhomboidal, with the infero-interior 

 angle slightly produced and with an angulation in the margin above. 

 From this point there is a thickening or ridge extending toward the 

 fixed end. Peduncle longer than the body of the tooth. Upper mar- 

 gin abruptly curved forward and marked by seven denticles, of which 

 the third inner one is usually the largest; the formula for this tooth 

 may be written 2 + 1+4. 



"Inner lateral tooth (Fig. 3) spoon-shaped, with the infero-interior 

 margin angular. Upper anterior margin marked with a fringe of about 

 twenty-four denticles, decreasing in length from the interior extremity. 

 Peduncle straight, wider than the body. 



"Outer lateral tooth (Fig. 4) falciform, straight along the peduncle. 

 Anterior margin and extremity denticulated with thirty minute denti- 

 cles, usually decreasing in length toward the distal extremity, but 

 subject to some variation. The denticulate margin extends more than 

 one-third the length of the tooth. Peduncles slender and nearly 

 straight. 



"The formula for the denticles is: 



4+ 1 + 4 

 30 - 24 - 7 - 1" T~ - 7 - 24 - 30. 



"There is a marked variation in the character of the denticles on the 

 intermediate and lateral teeth. On the intermediate they are large, 



* It is proposed by Mr. Beecher and the senior writer to give to this tooth the name of 

 admedian. In a forthcoming- monograph of the Rissoida that name will be constantly so em- 

 ployed. 



