426 EXPLANATION OF PLATES. 



43. Lepeta (Cryptobranchia) concentrica, Micld. Oregon. 



0, mantle-edge ; P, muscle ; X, intestine ; Z, genital 

 and anal papilla, ....... 331 



44. Acmsea mitra, Esch. California, 331 



45. 46. Acmsea (Collisella) spectrum (Nuttall) Keeve. Cal., 331 

 4t. Acmsea (Collisella) variabilis, Sowb. Valparaiso, . 331 



48. Scurria scurra, Lesson. W. Coast of S. America, . 332 



49. Patella cserulea. Lam. Teneriffe, 333 



50. Patella (Helcion) pectinata, Linn. Cape of Good Hope, 334 



51. Patella (Patina) pellucida, Linn. England, . . . 335 



52. Patella (Metoptoma) Solaris, de Koninck. Carb., Eur., 335 



53. 55. Chiton olivaceus, Sowb. A, anterior, B, middle, 



C, posterior valve, seen from outside ; i), IJ, F, the 

 same valves, from within ; g, sinus jugali, between the 

 two anterior sutural laminae ; h, /i, dentes, or teeth 

 between the notches or slits in the laminae of inser- 

 tion ; I, k^ slits in lamina of insertion ; Z, outer end 

 of line separating the area lateralis of the middle 

 valve from the area centralis ; m, end of the line sep- 

 arating the central area of the tail-plate from the 

 posterior portion ; the angulation of this line in the 

 median line of the animal forms the mucro, . .336 

 56 (and 54, Plate 85). Chiton niger, Barnes, yl, anterior valve, 

 from above, showing the laminae of insertion and 

 notches; P, the middle valve, from above; g^, sinus 

 jugali, in front of the jugum, or area jugali, and 

 between the two sutural laminae ; i, Z, notches between 

 the sutural and insertional laminae, and forming the 

 ends of the line forming the anterior border of the 

 lateral and posterior border of the central areas ; 

 (7, tail-plate ; g, sinus jugali ; m, end of line sepa- 

 rating the areas ; D, anterior valve, from within, show- 

 ing teeth (h, h) and notches of laminae of insertion ; 

 U, middle valve, from within ; gr, jugal sinus, between 

 the- sutural laminae ; i, notch, between sutural lamina 

 and side-lamina of insertion, 836 



Plate 85. 



54. Chiton niger, Barnes. (Explanations as abave), . . 336 

 5T. Chiton squamosus, Linn. West Indies, . . . 338 



58. Chiton (Helminthochiton) Griffithii, Salter. Silurian, 



Ireland, 339 



59. Chiton (Chonechiton) viseticola, Ryckholt. Carb., 



Belgium, 389 



64-66. Chiton (Priscochiton) Canadensis, Billings. Lower 



Silurian, Canada, ..... . . 339 



