374 Annals of the Carnegik Museum. 



to the Pseudosphicrexoclius group, as the eyes are close to the glabella. 

 Cheinirus mercurhis Billings is so close to C. viilcanus and prolificus, 

 that it is difficult to separate it specifically and certainly belongs to 

 PseiidospJurrexoclius. 



The group referred to Schmitt's subgenus NieszJunvskia, is an homo- 

 geneous one, including those species with spiniform projections on the 

 glabella or with very high ])Osterior elevations of the glabella. As 

 thus defined, however, the group produces the anomaly of putting 

 Cheininis viilcanus in the genus PseiidospJuvrexocJuis and the variety 

 Cheinints 7'iiliaiuis billingsi in the ^^<exiMi Nieszkowskia. 



The group referred to SpJuerocorpJie is evidently correctly made up, 

 and to it should be added Splicer oco)phe major Ruederman and 6". good- 

 iiovi Raymond. 



The last division, Pseudosphcerexochus, must be somewhat modified 

 to include Clteirurus inikaniis Billings, Pseiidosphcerexochus trentoneusis 

 Clarke, P. chazyensis Raymond P. approxiniiis Raymond and Pseu- 

 dospJucrexoiJiiis viilcanus billingsi. 



In the group there is a series of forms of which Ceraunis (sensu 

 stricto) is the most primitive, tending from that genus to SphccrexocJiiis 

 by a constant decrease in the size of the fixed cheeks, an increase in 

 the relative size of the free cheeks, a great increase in the relative size of 

 the glabella and a gradual decrease in strength of the two anterior gla- 

 bellar furrows. This variation is accompanied by a constant decrease 

 in size. 



Sphcerocorphe is evidently a specialized offshoot in which the bulbous 

 condition is carried, in some measure, to an extreme, and this form 

 is not in the direct line, which would seem to pass through a form like 

 Chein/rus viilcanus to forms like SplusrexocJius parvus. 



Nieszkowskia is a senile expression of Pseudosphivrexochus and not to 

 be considered in the line, except as an offshoot. 



In Clarke's classification too much importance is given to the 

 shape of the glabella and the direction of the glabellar furrows. 

 These are very variable with each natural group, as, for instance, in 

 Ceraurus (as restricted). The glabella may be either quadrate or ex- 

 panded toward the front, while in Pseudosphccrexochus it may be sub- 

 triangular or quadrate. The posterior lobe of the glabella may be 

 isolated in Ceraurus, Pseudosphitrexochus, Sphcerexochus zx\<\ Crotalo- 

 cepliahis. 



Taking, however, for the imjjortant characters, the position of the 



