PLATE XVII., AGNOSTUS AND MICRODISCUS. 
Fic. 1. Agnostus levigatus, Dalm., var. terranovicus, n. var. a, head 
shield. 6, pygidium. Mag. 4. From Div. 1 d?, Highland Cove, New- 
foundland. See p. 233. 
Fic. 2. A. levigatus var. mammilla, n. var. a, head shield. 0b, pygidium. 
Mag. +. From Div. 1 d?, Highland Cove, Newfoundland. See p. 235. 
Fia. 3. A. levigatus var. ciceroides, n. var. a, head shield. 3, pygidium. 
Mag. +. Found with the preceding. See p 234. 
Fic. 4. Microdiscus Schucherti n. sp. a, head shield. 0, pygidium. 
Mag. +. From Olenellus limestone, Troy, N. Y. See p. 238. 
Fia. 5. Miecrodiscus Dawsoni, Hartt. a, head shield. 6, same in profile. 
c, pygidium. Mag. 7. d, young larval stage, head shield. Mag. 12. 
e, next larval stage, head shield. Mag. 1°. All from Div. 1 c!, St. John, 
N. B. Seep. 240. 
Fic. 6. Microdiscus speciosus, Ford. head shield. Mag. ?. From 
Olenellus limestone, Troy, N. Y., figured for comparison. See p. 236. 
Fia. 7. Microdiseus precursor. Head shield. Mag. ?. From Div. 1 ¢’, 
St. Martin’s, N. B. See p. 239. 
Fia. 8. Mierodiseus pulchellus Hartt. a, head shield. 6, same in profile. 
ec, pygidium. Mag. +. ad, embryonic or Protaspis stage. Mag. 4). 
e, early larval stage. jf, pygidium of same. Both Mag. 2°. All from?Div. 
1d', St. Martin’s, N. B. See p. 242. 
