viii YORKSHIRE TYPE AMMONITES— II Nov 



1913 



This genus is near to Derolytoceras, Rosenberg, 1909, but is dis- 

 tinguished by rursi- instead of prorsi -radiation, less massive eostae and 

 more massive whorls. The two genera would appear to be offshoots 

 of the same stock, and Derolytoceras is the first to appear. 



The genus is somewhat like Pachylytoceras, S. Buckman, 1905, 144 ; 

 but the rings are distinct and rib-like : they are not heavy corrugations. 

 Derivation, Tpa\vs, rough. 



Genus, TILTONICERAS, nov. 

 Type, T. costatum, nov. 



Platycones like Vacekia, S. Buckman, with excessively long peripheral 

 projection of radial line. Carina very prominent, but on cast small. 

 Septicarina ? no partition-band or impression seen. Carina filled with 

 callus ? Carina in costate species notched at intervals by continuation 

 over it of intercostal depression ; in striate stage notches approximate 

 and subcrenulation is developed. 



Distinct from Vacekia by having hardly any lateral curve of radial 

 line and by lacking a tabulate periphery. 



The genus is erected for the series of Harpoceras acutum, Tate 

 (Wright). 



T. costatum differs from T. acutum in being more distinctly and 

 strongly costate : it gives the radial line more clearly. The genotype 

 will be figured at an early opportunity. 



Family Hildoceratidae. Name from Tilton, Leicestershire, the 

 locality of the genotype. 



Genus, ELEGANTULICERAS, nov. 

 Type, Am. eleganttdus, Young & Bird 



Like Tiltoniceras, but rostration much less, and carina smaller. 

 Septicarina suggested by type : in Am. ovatulus, Simpson, mark of 

 partition-band is distinct. 



There is superficial likeness to Tiltoniceras. It is important 

 geologically to mark the differences, as this series occupies another and 

 higher horizon. 



Genus, ELEGANTICERAS, nov. 

 Type E. pseud o-elegans, nov. 



Like Elegantuliceras, but radial line more rostrate, and more 

 curved laterally ; ribs broader ; carina less defined. 



The genus is for the series of Am. elegans, Young & Bird, 1822 (non 

 Sowerby, and non Y. & B. 1828) = E. pseudo-elegans, nov. An example 

 which will be figured to be type of genus and species. 



This genus and Elegantuliceras differ from Pseudolioceras by having 

 ribs which are true costse, not striicostae : in Pseudolioceras a costate 

 stage on outer area is associated with a striate stage on inner part. 

 Further, in these genera a complete striate stage is developed while 

 the umbilicus is still gradate. 



