212 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Thorax with 12 segments, axial lobes convex, relatively narrow; 

 pleural lobes broad, flattened for about one-half their width from 

 the axis, then arching gently downward and backward to their 

 pointed ends ; pleural furrows nearly as wide as the segment for 

 about one-third of its length, where they narrow and disappear 

 some distance within the falcate termination of the segment. 



Pygidium small, strong, convex; axial lobe broad, convex, and 

 about three-fourths the length of the pygidium; it is divided by 

 narrow, deep transverse furrows into three segments and a terminal 

 section ; pleural lobes rising abruptly from the margin and curving 

 gently to the dorsal furrow about the axial lobe; pleural furrows 

 shallow and curving backward towards the base of the lateral spine 

 that originates on each side opposite the posterior half of the axial 

 lobe and within the outer margin ; these spines have a strong base 

 that merges into the side of the pleural lobes in such a manner as to 

 give the impression that they were formed by the continuation 

 outward and backward of three of the anchylosed segments of the 

 pygidium. The strength and curvature of the spines vary somewhat, 

 but as a rule they are much like those of figures i, 10, plate 30. 



Surface of test finely punctate with strong scattered granulations 

 over free and fixed cheeks, frontal limb and border, and raised 

 portions of thoracic segments and pygidium ; on the glabella a few 

 rather large, low tubercles are scattered over the surface. Some 

 specimens have a rather fine, even granulation over the glabella 

 and other parts of the cephalon. 



Measurements. — This is one of the largest trilobites known to me 

 from the Cambrian above the " Olenellus " zone and below the 

 Dikelocephalus zone with the exception of Paradoxides of the Atlan- 

 tic Coast province. Fragments of the cephalon and thorax indicate 

 a length of 21 cm. exclusive of the long spines of the pygidium. The 

 proportions of an entire dorsal shield are shown by figure i, plate 30. 



Observations. — -I have hesitated to identify the Alabama form with 

 that from Texas, owing to the large size the latter attains, but with 

 specimens of the cranidium of the same size the similarity is so great 

 that there does not appear to be sufficient reason to distinguish them 

 as distinct species. The greater proportional broadening of the 

 frontal border of the cranidium with increase in size of the cephalon 

 gives ah appearance to the large cephala that is of specific importance 

 unless the broadening with growth is considered. There is also 

 widening of the base of the glabella in the Texas forms that is seldom 

 seen in those from Alabama, but this is not persistent; the more 



