168 SHIMER AND GRABAU HAMILTON GROUP OF THEDFORD 



septum in the calyx is 10 or more, decreasing in strength toward the 

 center. 



Another young individual, in which the carinas are weakly developed 

 in a calyx about 25. millimeters in diameter, was sectioned about 20 

 millimeters below the calyx. The greatest diameter of the section is 9 

 millimeters ; carinas are absent, though in a few septa slight thicken- 

 ings near the margin indicate the beginning of these carinas. 



A cylindrical specimen, also young, has a diameter of about 20 milli- 

 meters at the calyx, and the septa supplied with carinse in the outer 

 zone, the central area of 10 millimeters diameter being free from them. 

 The fossula is well developed. A section of the early stage with the 

 greatest diameter of 12 millimeters shows a single well developed carina 

 on each septum just within the peripheral margin, and on some of the 

 septa another carina within this, or a slight thickening marking the 

 beginning of a second carina. The four primary septa join in the center. 

 Another section 23 millimeters in diameter shows the peripheral zone 

 supplied with 4 or more rows of carinas and a few weaker ones nearer 

 the center. 



A more accelerated individual shows in a section 13 millimeters in 

 greatest diameter as many as 7 carinas on the septum, the strength de- 

 creasing toward the center, while another of the same diameter shows 

 only 2 or 3 carinas on each of the larger septa. 



It thus appears that in individuals which are highly accelerated the 

 carinas appear early in life, while in others they appear late. In some 

 individuals, which are but little removed from the ancestral Cyathophyl- 

 lum, the carinas may not appear until the adult stage is reached. This 

 gives us a basis for specific differentiation. H. halli is accelerated, the 

 carinas appearing early. The more primitive types should be separated 

 specifically from this species. Now, instead of deriving an argument 

 for generic union from this evident relationship, we have a good basis 

 for generic separation. Beyond question, Heliophyllum as represented 

 by H. halli has been derived from Cyathophyllum, for in its youthful 

 stages it still retains the characters found in the adult of typical Cyatho- 

 phyllum, such as C. helianthoides Goldfuss ; but it has passed beyond 

 the Cyathophyllum stage and acquire^ new characters in the carinas, 

 and therefore in any refined phylogenetic classification is entitled to 

 generic rank. 



LEIORHYNCHUS MULTICOSTUS HALL, L. LAURA BILLINGS, AND L. HURONENSIS 



NICHOLSON 



A number of well preserved specimens of Leiorhynchus were obtained 

 from a calcareous bed above the Encrinal limestone, but the exact posi- 



