208 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



DESCRIPTION OF PLATE 24 



PAGE 



Neolenus serratus (Rominger) 190 



Fig. I. (Natural size.) A partly exfoliated specimen, showing (a') 

 an antenna, numerous thoracic legs (thl), and jointed caudal 

 rami (cr). The caudal rami have been dragged backward, 

 pulling with them a portion of the under edge of the ventral 

 lining of the body cavity. U. S. National Museum, Catalogue 

 No. 57656. 

 la. (Natural size.) Pygidium with the caudal rami extending out 

 from beneath it in their probable natural position. U. S. 

 National Museum, Catalogue No. 57657. 



Ptychoparia cordillercB (Rominger) 190 



Fig. 2. (X6.) Dorsal view of a specimen from which the dorsal shield 

 has been removed, leaving the branchiae (br) exposed ; also 

 a few of the thoracic legs (thl). U. S. National Museum, 

 Catalogue No. 57658. 



Mollisonia symmetrica Walcott 196 



Fig. 3. (Natural size.) Dorsal view of the type specimen found in the 

 Stephen formation on Mount Stephen above Field, locality 

 (14s). U. S. National Museum, Catalogue No 57659. 



Tontoia kwaguntensis Walcott I99 



Fig. 4. (X2.) Dorsal view of a cast made in the natural mold, which 

 is the type specimen. From the Tonto sandstone, Kwagunt 

 Valley, Grand Canyon, Arizona, locality (73). U. S. National 

 Museum, Catalogue No. 57660. 



Mollisonia gracilis Walcott 197 



Fig. 5. (X2.5.) Dorsal view of the type specimen of the species and 

 genus. The specimen is laterally compressed. U. S. National 

 iMuseum, Catalogue No. 57661. 



Mollisonia ? rara Walcott 198 



Fig. 6. (Natural size.) A fragment of this species, showing the form of 

 the ends of the thoracic segments. U. S. National Museum, 

 Catalogue No. 57662. 

 7. (X2.) A small crushed specimen, showing a portion of the 

 cephalic shield, thoracic segments, and pygidium. U. S. 

 National Museum, Catalogue No. 57663. 



The specimens represented by figures i, la, 2, 5, 6, and 7 are from locality 

 (35k) Middle Cambrian : Burgess shale member of the Stephen formation, 

 on the west slope of the ridge between Mount Field and Wapta Peak, one 

 mile (1.6 km.) northeast of Burgess Pass, above Field, British Columbia. 



