34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



Lower Caml)rian, Mount Whyte ; (loc. 6id) southwest slope Mount 

 Shaffer, British Columbia. 



IIoIotypc.—U.S.^M. no. 64387. 



LONCHOCEPHALUS Owen, 1852 



Lonchocephalus verrucosus (Whitfield) 



Conoccphalites vcvntcosus Whitpield, Amer. Mus. Nat. Hist. BuH. i, p. 146, 

 pi. 14, figs. 9-12, 1884. 



Upper Cambrian, Potsdam; near "Post office." Ausable Chasm, 

 New York. 



CoO'/'^-^— A.M.N. H. no. 280. 



MENOMONIDAE Walcott 



MENOMONIA Walcott, 1916 



Mcnomonia Walcott, Smithsonian Misc. ColL, vol. 64, no. 3, p. 161, 191 6. 

 MUlardia Walcott, idem, p. 163, 1916. 



Walcott referred three genera to the Proparian family Menomo- 

 nidae, but he failed to recognize that two of them were identical. 

 Evidence for a primitive aspect about Mcnomonia and Drcsbachia 

 may be questioned. Evidently Walcott based his idea of this on the 

 numerous thoracic segments of M. calynicnoides. Examination of 

 available specimens fails to prove that this extraordinarily long thorax 

 belongs to Mcnomonia, although association in three instances sug- 

 gests the possibility. Even if the genotype has 42 thoracic segments, 

 one can hardly consider this alone as evidence of primitive structure. 



It seems rather that the Menomonidae are a highly specialized 

 group descended from species now placed in Alokistocarc. 



Menovwnia is a characteristic trilobite of the early Upper Cam- 

 brian Ccdaria zone; thus far being confined to that zone. Whitfield's 

 original specimens of the type species are on small pieces of rock 

 with the types of Ccdaria woosfcri. 



MUlardia was distinguished from Mcnomonia by differences of 

 brim and in having fewer thoracic segments. There is a difference 

 in the brim of AI. calymcnoidcs and of M. scmclc but it involves no 

 altered structure and the gap between the two species is bridged by 

 intermediate forms. M. calymcnoidcs has a much swollen brim, 

 whereas other species obtain the same rigidity by arching the short 

 brim. Many specimens referred to MUlardia retain the libragenes, 

 giving them a different aspect, which caused their reference to a 

 separate genus. 



Drcsbachia is a distinct, but closely related genus. Compared with 

 Menomonia, the glabella is essentially the same but the fixigenes are 



