EXPLANATION OF THE PLATES. 311 



48. Sinusigera cancellata, dentition, .... 12*7, 130 

 4W, 50. Echinospira diaphana, Kr. Within the temporary 



shell, in fig. 49, is seen the permanent shell (Marsenia). 



(Krohn), 127 



51. Calcarella spinosa, Souleyet, ..... 12T 



52. Larva of Rissoa costata. (After Loven.) The velum 



has not yet disappeared, although the foot is 

 developed, ....... 127, 14 



53. Embryo of Pneumodermon violaceum, d'Orb. (Gegen- 



bauer.) The otocysts are seen by transparence, . 131 



54. Embryo of Dentalium Tarentinum, Lam, (Lacaze- 



Duthiers. ) ^, flagellum ; Z, velum; m, posterior 

 mantle-opening; c, primitive shell formed of two 

 parts, . . . . . . . . .131 



55. The same, prior to the formation of the shell. /, crown 



of cilife ; ^, flagellum ; m, posterior mantle opening, 131 



Plate 21. 



56, 57. Embryo shell of Margaritana rugosa. (Lea, Obser- 

 vations, vi, t. 5, f. 26, 26 a), . ". . . 131,132 



58. Very young embryo of Modiolaria marmorata, Forbes, 



greatly magnified. (After Loven.) cZ, disk, with 

 ciliated border ; /, flagellum ; v v, valves ; m ciliated 

 mantle, ......... 131 



59. Young of My tilus edulis, Linn. (After Loven.) e, eye ; 



e', auditive capsule ; 1 1, labial tentacles ; s s, stomach ; 

 6, branchijB ; h, heart ; v, anus ; Z, liver ; r, renal 

 organ ; a, anterior adductor ; a', posterior adductor ; 

 /", foot. The arrows indicate the afferent and efferent 

 openings ; between them the mantle leaves are united 

 in the young, ........ 131 



60. Embrj^o Oyster, m, month, commvmicating with a 



ciliated digestive cavity ; e c, ectoderm ; a, anal 

 papilla ; u, vellum. (Brooks), . . . 131, 132 



61. Embryo Oyster, more advanced, with valves extended ; 



?' s, Z s, right and left valves of the shell ; an, anus ; 

 a, anal papilla ; ma, mantle ; u, velum ; b, body-cavity ; 

 •s-Z, stomach. (Brooks), . . . . ' . 131, 132 



62. Dorsal view of an embryo oyster six days old, swimming 



by the cilia of its velum. (Brooks), . . 131, 132 



63. Right side of an embryo oyster six days old. m u, 



muscles ; Z, liver ; i;, velum ; 6, body-cavity ; m, mouth ; 

 an, anus ; st, stomach ; s, shell. (Brooks), . 131, 132 



