OF SHELL-FISH AND CRUSTACEA. 197 



appearance at the back of the head. The stomachs may be 

 detached with the point of a knife, and when some 12 or 20 or 

 more (as the deposit obtained from them is small) have been 

 collected, they should (taking care that the skin of each stomach 

 is cut or broken) be boiled for a few seconds in a weak solution of 

 washing-soda or ammonia, and then immediately be thrown into a 

 beaker of cold water. By these means we get rid of grease, etc., 

 and render the subsequent treatment by acids more easy. The 

 empty skins of the stomachs will float and may be picked out of 

 the solution. 



The residue which collects after the solution has stood for 

 some time should first be washed free from alkali, and then treated 

 with acids in the usual manner. It is unnecessary to enter into 

 the details of the cleansing of the deposits, as a reference to Mr. 

 Griffin's articles in this Journal,''^ or some of the many books on 

 the subject, will supply all requisite information. 



With regard to the specimens to be met with in these opera- 

 tions, I may remark that in a gathering from the stomachs of 

 shrimps caught off Flushing, in March, 1884, I have obtained 

 large specimens of Eiipodiscus argus, Cosci?iodiscus^ Aditioptychus 

 imdulatiis, Acthiocydus Ralfsii and others, Trice7-atiiim^ Biddul- 

 phia rhombus, and in larger numbers than any of these a beauti- 

 ful circular form, with several rays, of which I have been unable to 

 find the name ; possibly, it is a species of AdhioptycJms. Amongst 

 the small forms, I have found the beautiful Doryphora atnphiceros 

 in great profusion. This last form I have met with more fre- 

 quently in the stomachs of shrimps than elsewhere. 



The method of separating deposits into different densities is 

 very useful here as with many other gatherings of diatoms^ inas- 

 much as the large forms are then more easily isolated. The often- 

 advised whirling in a large evaporating dish in order to separate 

 the diatoms from sand and debris may be frequently practised 

 with success. In the washings of all diatoms I have found it of 

 the utmost advantage to perform the later rinsings in distilled 

 water. The diatoms are thus more effectually cleaned from salt, 

 etc., and present less attraction to moisture in the case of dry 

 mounts. 



* See this Journal, Vol. III. p. 229. 



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