124 IGERNA B. J. SOLLAS. 



alone are coloured ; so that in this case there is a curious 

 reversal of the usual relative behaviour of these stains. I 

 have not found any other case in which Bethe's stain will 

 colour in section a structure which has an affinity for the 

 ordinary staining reagents^ though this is commonly the case 

 in working with material in bulk. 



The above description refers to Patella vulgata; it is 

 equally applicable to P. pellucid a, as well as to a number 

 of other species of Patella sent me by the kindness of Pro- 

 fessor Mitsukuri^ and probably to all species of Patella. To 

 Professor Mitsukuri I am also indebted for specimens of 

 Nacella. the teeth of which, isolated by boiliug in fuming 

 nitric acid, are shown in Fig. 6. The marginals, as in 

 Patella and all Docoglossa examined, do not contain a sili- 

 ceous skeleton ; they dissolve completely in nitric acid and 

 ai'e consequently not represented in the figure. 



Cryptobranchia. 



My thanks are due to Mr. Rathbun, of the United States 

 National Museum, for specimens of Cryptobranchia con- 

 ceutrica. The lateral and central teeth possess a skeleton 

 of siliceous pieces which are fused in each row into a single 

 plate, but it is possible in this plate to detect outlines which 

 seem to mark the limits of once separate teeth. Apparently 

 there were three laterals and one central, the central tooth 

 being much reduced. In the darkly coloured cusps the line 

 of demarcation between the outer and inner laterals is clear, 

 but the two inner laterals of each side are closely fused 

 together (text-fig. 2). 



ACMAEA. 



Specimens of Acmaea virginea were obtained from 

 Plymouth. I owe to the kindness of Dr. Harmer examples of 

 Acmaea saccharina, as well as of many other molluscs. 

 Marginals being absent in this genus the greater part of the 

 radular substance is silica; the solution of the organic matter 



