DESCRIPTION OF GENERA AND SPECIES. 173 



connection with the illustration given by Doctor Owen leads me to think that the 

 genotype was a fragment of the cranidium of Owen's Dikelocephalus granulosus, 

 illustrated by figure 7, plate i [Owen, 1852]. This, however, can not be proven, 

 so I will accept Owen's definition and include under the genus a group of species 

 having a strongly convex glabella, with a narrow frontal limb and border and 

 broadly rounded front; tumid fixed cheeks, small eye-lobes, granulated surface, and 

 very faint or no glabellar furrows. 



The species are more or less provisionally referred, as only the central portions 

 of the cephalon are preserved. Further study, or the study of more perfect speci- 

 mens, will undoubtedly lead to the reference of some of them to other genera. 



Neither of the species referred to Menocephalus by E- Billings appears to belong 

 to the genus. They are: 



Menocephalus sedgwicki Billings [18656, p. 407] = Soleno pleura; 

 Menocephalus glabosus Billings [18656, p. 408] = Solenoplcura. 



Menocephalus salteri Devine [Billings, 18650, p. 203] is the type, an undescribed 

 genus. 



Menocephalus abderus (Walcott). 



Plate 16, Figure 3. 



Solcnoplcura abderus WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxtx, p. 88. (Species characterized 

 as below.) 



This species is represented by the glabella, occipital ring, fixed cheek, and 

 frontal rim. It is most closely related to M. acanthus, but differs in the nar- 

 rower fixed cheeks and short, rounded frontal rim. The surface is also marked 

 by larger and many more pustules, which are scattered more or less irregularly 

 over the surface. Three pairs of short glabellar curves are faintly indicated upon 

 the rounded sides of the somewhat convex glabella. The type specimen has a 

 length of 8 mm. and a large cephalon associated with it of 12.5 mm. 



Formation and Locality. Middle Cambrian: (C19) Uppermost layers of the 

 Ch'ang-hia limestone [Blackwelder, igo-ja, p. 33 (part of last list of fossils)], at 

 Ch'ang-hia, Shan-tung, China. 



Collected by Li San. 



Menocephalus acanthus (Walcott) . 

 Plate 1 6, Figures 4, 40-6. 



Solenopleura acantha WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 88. (Species described as 

 below.) 



General form of cephalon, exclusive of free cheeks, transversely rhomboidal, 

 and rather convex. Glabella prominent, convex, truncato-conical, with width at 

 the base and length about the same; a short, strong furrow marks off two small, 

 subtriangular lobes at the postero-lateral angle; a second pair of slightly marked 

 furrows occurs upon the sides, next to the dorsal furrow, about midway of the length 

 of the glabella ; the sides slope inward from the base, so as to reduce the width of 

 the rounded front to about two-thirds that of the base; occipital furrow narrow, 

 transverse, and deep; occipital ring narrow at the sides, broadening toward the 

 center, where it is thick and convex; dorsal furrow very distinct at the sides and 

 front. 



Fixed cheeks convex, but much lower than the glabella; they are about as 

 wide at the palpebral lobe as the width of the glabella in front ; their appearance 

 of convexity is given by the downward slope toward the frontal rim and backward 



