38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Thorax : mm. 



Length " 24 . oo 



Width 30.00 



Width of axial lobe at first segment 10.00 



Width of pleural lobe at first segment 10.00 



Pygidium : 



Length 18.00 



Width 26 . 00 



Width of axial lobe at anterior ring 9.00 



Width of axial lobe at posterior ring 6.50 



Hypostonia : 



Length 29 . 00 



Length of body 26 . 00 



Width 18.00 



Width at base 23 . 00 



Width at junction with head 33.00 



Greatest width of body 19.00 



Observations. — This species attains a large size. A cephalon and 

 six thoracic segments has a length of 73 mm., a width of thorax of 

 70 mm. ; with the seventh segment and the pygidium, exclusive of 

 spines, the entire shield would have had a length of 107 mm. 

 Fragments occur that indicate even a larger size. 



Neolenus superhiis and the associated Neolenus inftatus have 

 many characters common to each ; both attain a large size, both have 

 small eyes, subquadrilateral glabellas, spinose genal angles, seven 

 thoracic segments, spinose terminations to pleural segments and 

 border of pygidium, occipital and thoracic median spines, lined 

 surfaces, and resemble each other in minor details. The two species 

 differ in the glabella of N. siipcrhns being slightly convex with 

 nearl}^ parallel sides, instead of being inflated and expanded toward 

 the front. The pygidium of A^ superbus has seven axial rings and 

 five spines on the border ; that of N. iniiatus has nine rings and eight 

 spines. Neolemis serratns (Rominger)^ has a broader dorsal shield, 

 falcate terminations to the pleural segments, four rings on the axis 

 of the pygidium, a subquadrangular glabella and genal spines that 

 are formed by the union of the outer border and posterior border, 

 instead of being a continuation of the outer border, as in A^. superbus 

 and A^. infJatns. The surface of N. serratns is granular and not 

 raised lines, as in N. superbus. 



Formation and Locality. — Middle Cambrian: 1,895-2,140 feet 

 (605-653.8 m.) below the L^pper Cambrian and about 2,000 feet 

 (609.6 m.) above the beds containing Zacanthoides typicalis Walcott 

 and Bathynriscus hozveUi Walcott, the horizon which is correlated 



* Ogygia serrata Rominger, 1887, Proc. Acad. Nat. Sci. Philadelphia, p. 13. 



