636 



INDEX 



free-cheeks in, 117. 

 geological history of, 120. 

 historical review of, Zittel, 111. 

 hypostoma in, Bernard, 188. 

 larvae of, 169. 



larval stages of, 122, 164, 166. 

 metamorphoses of, Barrande, 166, 

 193. 

 Callaway, Ford, Matthew, Sal- 



ter, Walcott, 166. 

 natural classification of, 109. 

 orders of development in, Barrande, 



167. 



phylembryo in, Jackson, 121. 

 protaspis in, 122. 

 stage of, 121. 



stages of, from Cambrian rocks 

 of New Brunswick, Matthew, 

 171. 



rank of, 114. 



structure and development of, 109. 

 systematic position of, 163. 

 Trimerelta, 243. 

 Trimerocephalus, 153, 156. 

 Trimerus, 154. 



glabella and pygidium in, 155. 

 Trinucleidse, 130, 131, 134. 

 defined, 138. 



primitive head structure in, 135. 

 Trinudeus, 113, 116, 130, 138, 147, 177, 

 178, 214, 220, 222. 

 appendages in, 223. 



in pygidium of, 135. 

 concentricus, 221 . 



pygidium of young, 223. 

 determination of sutures in, Bar- 

 rande, 134. 

 endopodites of, 224. 

 exopodites of, 224. 

 eye-line in, 223. 

 -spots in, 135. 



in young, 137. 

 -tubercle in, 221. 

 fixed-cheeks in, 127. 

 free-cheeks in, 124, 135. 

 fringes on exopodites of, 218. 

 hypostoma in, GEhlert, 135. 

 intestinal canal in, 209. 

 lines on cephalon of, 118. 

 omatus, 177. 

 pitted border in, 138. 

 pygidium in, 135. 



structure and appendages of, 220. 



triangular areas in adult, 222. 



in young, 222. 

 Triopus, 133. 

 Triplecia, 245. 

 Triplesia putillus, 334. 

 Tripocalpis triserrata, spines in, 48. 

 trocholophian stage, 278. 

 Trochurus, 150. 



Trophon magellanicus, spiniform prom- 

 inences on, 46. 

 Tropidocoryphe, 148. 



eyes in, 148. 



fixed-cheeks in, 148. 

 Tropidoleptus, 231, 246. 



zugolophus stage in, 281. 

 Truncatulina reticulata, spines in, 49. 

 Tulotoma, differentiation in, 66. 

 typembryo, 121, 247. 



Uncinulus, 246. 



Stricklandi, 314, 315. 

 Uncites, 246. 

 Ungulates, development of horns in 



horned, 47. 

 Unio spinosus, anchoring spines on, 



Simpson, 46. 

 Uralichas, 150. 

 use and disuse, law of, 28. 

 Uvigerina aculeata, spines in, 49. 



asperula, spinules in, 49. 



valves in Brachiopoda, difference in, 



234. 

 variation, free, 35. 



among Mollusca, 65. 



in Achatinellae, Hyatt and 



Verrill, 36. 

 law of, 5. 

 manner of, 6. 

 mechanical, 6. 

 molar, 6. 

 molecular, 6. 

 physico-chemical, 6. 

 progressive, 6. 



