yiii EXPLANATION OF THE PLATES. 



C. aculus, Transverse line of the thorax, fig. 1 24 ; var. A, fig. 1 25. 



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



Form II., fig. 122. 

 Inner sexual parts of the female, fig. 123. 

 Annulus ventralis of the female, fig. 126 ; the same, inner side, fig. 127. 



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

 enlarged, fig. 134. 



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



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



Inner sexual parts of the female, fig. 139. 



Plate III. a, lamina antonnalis ; b, epistoma ; c, the exterior spine of the second joint of the exterior 

 antenna. (The letters are only indicated in fig. 140.) 



Gambarus. Group I. 



C. Blandingii (Type), fig. 140. C. troglodytes, fig. 141. C. Clarkii, fig. 142. C. acutus, fig. 143. 

 C. acutus, var. B, fig. 144. C. Lecontei, fig. 145. C. angustatus (Type), fig. 146. C. spicu- 

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

 Wiegmanni, fig. 151. 



Cambarus. Group II. 



C. affinis, fig. 152. C. propinquus, fig. 153. C. obscurus, fig. 154. C. virilis, fig. 155. C. extra- 

 neus, fig. 156. C. juvenilis, fig. 157. C. placidus, fig. 158. C. lancifer, fig. 159. C. immunis, 

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



Cambarus. Group III. 



C. latimanus, fig. 162. C. obesus, fig. 163. C. advena, fig. 164. C. Carolinus, fig. 165. C. Bar- 

 lonii, fig. 166. C. robustus, fig. 167. 



Astacus. 

 A. nigrescens, fig. 168. A. Klamathensis, fig. 169. A. Gambelii, fig. 170. A. Trowbridgii, fig. 171. 



Plate IV. 



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



Plate V. 



Cambarus affinis, Fern. (nat. size). 



Plate VI. 



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



Plate VII. 



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



Plate VIII. 



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



Plate IX. 



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



Plate X. 



Astacus Trowbridgii, Fern. Type (nat. size). 



Plate XI. 



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



