No. 4.] BILLINGS — ON FOSSILS. 235 



8. Z. GENITIVA. — Corallum turbinate, curved, expanding to 

 ■a width of 21 lines in a lenijth of 4J- inches. Surface with a 

 few rounded folds of growth. Septal stria3 8 or 9 in the width 

 of o lines at the base; in the upper part where the surface is 

 perfect the striae are not visible (in the specimen examined), but 

 where a little worn there are about 6 in 3 lines, indicating both 

 the large and small septa ; or 3 where only the large septa are 

 represented. At a diameter of 18 lin^s there are 56 large septa, 

 '6 or 7 lines in depth; some of them reach nearly to the centre. 



The small septa are two or three lines in depth. The bottom of 

 ■the cup is smooth with a slightly elevated, low pyramidal colu- 

 :inella, forming a low ridge in the direction of a line drawn 

 through the fossette. The latter is large, ovate, the smaller ex- 

 tremity pointing outwards. Occurs in the Corniferous. 



9. Z. SUBRECTA. — Corallum somewhat straight, flexuous, 

 gradually expanding to a diameter of 21 lines in a length of 6 

 inches. Surface with rounded folds of growth and a few broad 

 undulations. Septal striae 9 in the width of 3 lines at the base, 

 becoming wider and more indistinct upwards. There are 38 

 large septa at a diameter of 18 lines, from 3 to 5 lines in depth; 

 small septa, in general from J to 1 line in depth. Occurs in the 

 Corniferous. 



Genus Heterophrentis (N. Gl.) 



Corallum simple, turbinate. Calice large with a well defined 

 septal fossette, the bottom either smooth or with a pseudocolu- 

 mella.=*= Septa below the calice sharp- edged, often with their 

 inner edges twisted together ; above the floor of the calice they 

 are usually rounded, especially on approaching the margin. 

 There is apparently only a single transverse diaphragm, and this 

 forms the floor of the cup. 



This genus is intended to include (more especially) such 

 species as R. spatiosa, H. excellens and some of tiiose referred to 

 JI. jji'oUJica = (^Zaphrentis proUficii). 



10. H. spatiosa. — This species I have heretofore called Zap>li- 

 rentis spatiosa. It is a short, rapidly expanding species. Length 

 of the typical specimen 3 inches, width at the margin 2 J inches, 



* For the sake of brevity, I shall hereafter make use of the word 

 ^columella. 



