viii 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; testieules 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. virllis, inner sexual parts of the Male Form I., fig. 128; side, fig. 129 ; testieules 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. 130; side, fig. 13G. 

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

 Inner sexual parts of the female, fig. 139. 



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

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



Cambarus. Group I. 



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

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

 lifer, fig. 147. C. pellucidus, fig. 148. C. penicillatus, fig. 149, ('. 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. exlra- 

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

 fig. 100 ; fig. d, var. of the epistoma. C. rusticus, fig. 161. 



Cambarus. Group III. 



C. latimanus, fig. 102. C. obesus, fig. 163. C. advena, fig. 104. C. Carolinus, fig. 105. C. Bar- 

 lonii, fig. 100. C. robustus, fig. 107. 



Astacus. 

 A. nigrcscetis, fig. 108. A. Klamathensis, fig. 109. A. Gambclii, fig. 170. A. Trowbridgii, fig. 171. 



Plate IV. 



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



Plate V. 



( 'ambarus ajfinis, Fein. (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 car. A. Cambarus immunis, hand. 



Plate IX. 



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



Plate X. 



Astacus Troujbridgii, Fein. Type (nat. size). 



Plate XI. 



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



