Shimer — Lower-Middle Cambrian Transition Fauna. Ill 



theory by the east and west strike and southern dip of the Mid- 

 dle Cambrian Hay ward Creek beds lying a short distance to 

 the southeast. 



Description of species. 

 Acrothele gamagei (Hobbs). 



The two individuals found agree very closely with the type 

 description. 



Ryolithes shaleri Walcott. 



Parts of several specimens of this species were found. They 

 represent individuals somewhat below the normal in size. 



Olenellus (Holmia) brbggeri Walcott. 



One individual was found. This includes most of the gla- 

 bella, and one eye-lobe. The eye-lobe is narrow, elongate, and 

 crescent shaped ; it begins to arch outward from the most 

 anterior glabellar furrow. The glabella in outline and furrows 

 is very similar to the type description. Its surface is covered 

 with " the inosculating, fine, raised fretwork that as far as known 

 is confined to the genus Olenellus."* 



Strenuella strenua (Billings). 



Our specimen consists of the characteristic ends of two 

 pleura. They belong without doubt to this species, as they are 

 similar in every respect to an individual described from the 

 Lower Cambrian of North Wey mouth. f 



f Strenuella strenua (Billings). Fig. 1. 



Referred to this species with extreme doubt is a specimen 

 that may be a thoracic axis. It 

 1 consists of eight strongly arched 



segments, and tapers to an unusual 

 degree for an axis. It bears a median 

 row of tubercles, one upon the cen- 

 tral portion of each fold, the series 

 becoming more marked toward the 

 broad end of the axis. The middle 

 of each fold is marked by the groove- 

 like line produced by the overlapping 

 of the anterior portion of the fold 

 upon the posterior. 



The evidence in favor of referring 

 this specimen to Strenuella strenua 

 is its marked convexity, the median 

 row of tubercles, and the presence of 

 the pleura of that species near it, 



though it is very doubtful if they are near enough to have 



formed part of the same individual. 



* Walcott, 10th Ann. Rept. U. S. G. S., part 1, p. 640. 

 f This Journal, xxiii, 199-201. 



