124 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



Page 

 and frontal views of cranidium, x2. 6-8, Pygidia, X4 (U.S.N.M. coll. 

 120) ; U.S.N.M. 144648, plesiotypes. 9, Cranidium, x2.5. 10, Free 

 cheek, X2 (coll. cnr720) ; U.S.N.M. 144649, plesiotypes. 11, Hypos- 

 tome, x3 (coll. cnr/15) ; U.S.N.M. 144650, plesiotype. 12, 13, Dorsal 

 and frontal views of cranidium, x4. 14, Free cheek, x4. 15, Hypos- 

 tome, x4. 16, Cranidium, X2. 17, Exfoliated cranidium, X2 (coll. 

 cns/16) ; U.S.N.M. 144651, plesiotypes. 



Figs. 18-21. Aphelaspis laxa Resser 80 



18, Exfoliated free cheek, xl-S. 19, Cranidium, x4 (coll. cns/16) ; U.S.- 

 N.M. 144643, plesiotypes. 20, Free cheek, xl.5. 21, Pygidium, x4 

 (coll. cnr720) ; U.S.N.M. 144644, plesiotypes. (See also pi. 13.) 



Fig. 22. Aphelaspis arsoides Rasetti, n. sp 94 



Pygidium, x3 (coll. cnt/20) ; U.S.N.M. 144680, paratype. (See also pi. 



11.) 



Figs. 23-25. Dytremacephalus sulcifrons Rasetti, n. sp 101 



Dorsal, lateral, and frontal views of cranidium, X4 (coll. cnw/14) ; 

 U.S.N.M. 144690, holotype. 



Plate 13 



Figs. 1-7. Aphelaspis hridgei Rasetti, n. sp 77 



1-3, Dorsal, frontal, and lateral views of cranidium, X3 (coll. U.S.G.S. 

 2804) ; U.S.N.M. 144635, holotype. 4, Cranidium, X3. 5, Free cheek, 

 X3. 6, 7, Pygidia, x3 (coll. U.S.G.S. 2804) ; U.S.N.M. 144636, para- 

 types. 



Figs. 8-15. Aphelaspis laxa Resser 80 



8, Cranidium, x3. 9-11, Dorsal, frontal, and lateral views of cranidium, 

 X4. 13, 15, Pygidia, X2. 14, Lateral view of cranidium, X2 (coll. 

 U.S.N.M. 120) ; U.S.N.M. 144645, plesiotypes. 12, Free cheek, x2 

 (coll. cnr720) ; U.S.N.M. 144644, plesiotype. (See also pi. 12.) 



Figs. 16-23. Aphelaspis arses (Walcott) 93 



16-18, Dorsal, frontal, and lateral views of cranidium, x4. 19, Cranid- 

 ium, X4. 20, Pygidium, X4. 21, Free cheek, x4. 22, Free cheek and 

 pygidium, x4 (coll. cns/4) ; U.S.N.M. 144676, plesiotypes. 23, Cran- 

 idium, X4 (coll. cnr/4) ; U.S.N.M. 144733, plesiotype. 



Plate 14 



Figs. 1-12. Aphelaspis rotundata Rasetti, n. sp 84 



1-3, Dorsal, lateral, and frontal views of partly exfoliated cranidium, 

 X2.8 (coll. cns/20) ; U.S.N.M. 144652, holotype. 5, 6, Exfoliated 

 cranidia, Xl-5. 4, Exfoliated hypostome, X4. 7, Free cheek, x3. 8, 

 Exfoliated free cheek, x3. 9, Exfoliated pygidium, x2. 10, 11, Lateral 

 and dorsal views of exfoliated pygidium, X2.5 (coll. cns/20) ; U.S.- 

 N.M. 144653, paratypes. 12, Pygidium attributed to the species, X3 

 (coll. cnq'74) ; U.S.N.M. 144654, paratype. 



Figs. 13-19. Aphelaspis palmeri Rasetti, n. sp 81 



13-15, Dorsal, lateral, and frontal views of cranidium, x2 (coll. U.S.- 

 G.S. 2970) ; U.S.N.M. 144646, holotype. 16, Free cheek, X3. 17, Partly 

 exfoliated cranidium, x4. 18, 19, Exfoliated pygidia, X4 (coll. U.S.- 

 G.S. 2970) ; U.S.N.M. 144647, paratypes. 



Figs. 20-24. Glaphyraspis declivis Rasetti, n. sp 42 



20-22, Lateral, dorsal, and frontal views of cranidium, x7.5 (coll. Oder 



