vili EXPLANATION OF THE PLATES. 



C. acutus, Transverse line of the thorax, fig. 124; var. A, fig. 125. 



Inner sexual parts of the Male Form I., fig. 120; testicules viewed from above, fig: 121. 



Form II., fig. 122. 

 Inner sexual jiarts of the female, fig. 123. 



Annulus veutralis of the female, fig. 12G ; the same, inner side, fig. 127. 

 C. Clarlc'd, development of the first abdominal leg in the male, 0.3 inch long, fig. 133; the knob 



enlarged, fig. 1 34. 

 C. virilis, inner se.xual parts of the Male Form I., fig. 128; side, fig. 129 ; testicules viewed from 

 above, fig. 132. 

 The same, in Form II., fig. 130; side, fig. 131. 

 C. Bartonii, inner sexual parts of the Male Form I., fig. 135 ; side, fig. 136. 

 The same in Form II., fig. 137 ; side, fig. 138. 

 Inner sexu.al parts of the female, fig. 139. 



Plate III. a, lamina antcnnalis ; 6, epistoma ; c, the exterior spine of the second joint of the exterior 

 antenna. (The letters are onlv indicated in tig. 140.) 



C.\Mn.\iu's. Group I. 



C. Blandingii (Type), fig. 140. C. tro//h,/yle^, fig. 141. C. ClarUi, fig. 142. C. acutus, fig. 143. 

 C. aculus, var. B, fig. 144. C. Leconlei, fig. 145. C. an<juslalus (Type), fig. 146. C fpicu- 

 lifer, fig. 147. C. pellucidus, fig. 148. C. jycnicillalua, fig. 149, C. versutus, fig. 150. C, 

 Wiei/maimi, fig. 151. 



Cambahus. Group II. 



C. ajjinis, fig. 152. C. prnpinquun, fig. 153. C. ohscurus, fig. 154. C. virilis, fig. 155. C. exlra- 

 neus, fig. 156. C. Juvenilis, fig. 157. C. placidus, fig. 158. C. lancifer, fig. 159. C. immuni.'i, 

 fig. 160 ; fig. (/, var. of the epistoma. C. rusticus, fig. 161. 



C.^MBARUs. Group III. 



C. latiinanus, fig. 162. C. nbesus, fig. 163. C. advena, fig. 164. C. Carolinus, fig. 165. C. Bar- 

 tonii, fig. 1G6. C. robustus, fig. 167. 



ASTACUS. 



A. nir/rcsccns, fig. 168. A. Klamathensis, fig. 169. A. Gambelii, fig. 170. A. Ti-owbridgii, fig. 171. 



Plate IV. 



Cambarus Clarkii, Male Form I. (nat. size). 



Plate V. 



Cambarus njffinis, Fem. (nat. size). 



Plate VI. 



Cambarus pellucidus, Male Form I. (nat, size). 



Plate VII. 



Cambarus adoena, Male Form I. (twice enlarged). 



Plate Vill. 



Cambarus virilis, Male Form I. (nat. size) ; a hand of var. A. Cambarus immunis, hand. 



Plate IX. 



Cajiibarus obesus, Male Form I. (nat. size). 



Plate X. 



Aslacus Trowbridijii, Fem. Type (nat. size). 



Plate XI. 



Aslacus Gambelii, Male. Type (nat. size). 



