OLENELLUS AND OTHER GENERA OF MESONACID^ 281 



pressed. Glabella convex, conical, and strongly lobed ; dorsal furrow 

 shallow and interrupted about the anterior lobe by a very narrow 

 second furrow that separates a narrow ridge from the glabella ; 

 the anterior lobe of the glabella tapers from the base toward the 

 narrowdy rounded front and its base is broadly wedge shaped, owing 

 to the backward slope of the anterior pair of furrows ; the second 

 and third lobes are united about the ends of the second pair of 

 furrows, while the fourth lobe is clearly defined by the occipital 

 furrow ; occipital ring convex, of uniform wddth. and without a 

 median node or spine. Palpebral lobe united to the postero-lateral 

 base of the anterior glabellar lobe by a narrow ridge ; it is about 

 one-third the length of the cephalon, and at its posterior end it is 

 distant about one-half of its length from the glabella ; opposite its 

 posterior end and adjoining the dorsal furrow next to the end of 

 the fourth glabellar lobe a Small prominent tubercle breaks the sur- 

 face of the area within the palpebral lobe. Cheeks gently convex 

 and divided only by a narrow intergen.al ridge that extends from 

 the base of the palpebral lobe diagonally outward to the posterior 

 marginal border about midway of its length. 



Surface. — The surface is similar to that of CaUavia crosbyi, ex- 

 cept that the meshes of the reticulated network of narrow ridges 

 are somewhat finer and more like those of the right side of fig. 7. 

 pi. 28, than the meshes on the left side. 



Dimensions. — A cephalon 24 mm. in length has a width at the 

 base of 47 mm. Length of glabella 17 mm.; width of glabella at 

 base 10 mm. Width of glabella at base of anterior lobe inside the 

 narrow outer ridge 7 mm^. Length of palpebral lobe 8 mm. Distance 

 of palpebral lobe from glabella at anterior end 2 mm. ; at posterior 

 end 6 mm. 



Observations. — Of this species only a few specimens of the ceph- 

 alon are known. Its outline is similar to that of CaUavia crosbyi. 

 except that in the specimens thus far seen the genal spines are very 

 much smaller, and there is no evidence of an intergenal spine. The 

 marginal rim is less distinctly defined than in C. crosbyi; the palpe- 

 bral lobes are sliorter ; and the glabella proportionally shorter, more 

 conical, and more distinctly lobed. 



CaUavia biirri differs from C. broggeri as it does from C. crosbyi, 

 and it does not have the great occipital spine of the former species. 



Formation and Locality. — Lower Cambrian: (gn) associated 

 with CaUavia crosbyi in the dark, purplish siliceous shale of .the 

 A\^eymouth formation on Pearl Street, North Weymouth, Norfolk 

 County, Massachusetts. 



