324 Notes of Diatomacese/Mwc? in the stomachs of Mollusca. 



Naviculece. Coscinodiscus eccentricus, Ehr. 



Navicula Hippocampus, Ehr. Actinocyclus undulatus, Bailey. 



Ceratoneis Closterium, Ehr. Actinoptychus senanus, Ehr. 



Coscinodiscece. . ,. . 



Coscinodiscus Patina, Ehr. 



C. lineatus, Ehr. Dictyocha gracilis, Kg. 



This list will afford some idea of the nature of the deposits 

 going on in the Aberdeen bay at the depth and distance from 

 land already mentioned. 



The following species were evidently in a living state : — Melo- 

 siera sulcata, M. Jurgensii, Synedra Icevis, Navicula Hippocampus, 

 Surirella ?, Coscinodiscus Patina, Actinoptychus senarius, and they 

 were also very common ; in this latter respect, however, they were 

 not superior to the Dictyocha and Doryphora. 



Of those enumerated, the following are usually met with in 

 freshwater: Fragilaria pectinalis, Diatoma flocculosum, Cocconeis 

 Pediculus, Cymbella maculata and Gomphonema pohliaforme ; they 

 were also much less abundant than the others. Their presence 

 is readily accounted for, when it is considered that two large 

 rivers, the Dee and Don, besides numerous smaller streams, 

 empty themselves into the bay. Mr. Thwaites informs me that 

 he has found the Meloseira sulcata both in fresh and brackish 

 water. Some of the species mentioned are not uncommon in the 

 mud of our harbour. 



Mixed up with the Diatomacea were numerous individuals 

 belonging to two or three forms of Foraminifera, also spiculse of 

 a species of Grantia and fragments of Ulvte, with particles of silex 

 in a finely divided state. 



Some of those enumerated have a very extensive distribution : 

 Meloseira sulcata has been found at Melville Island, and by 

 Dr. Hooker at Victoria Barrier, where Coscinodiscus eccentricus 

 and C. lineatus also occur. These and others are abundant in 

 guano from Africa and Peru, and are now in myriads mixed with 

 the soil of our fields, and their presence may perhaps at a future 

 time be a puzzle to some assiduous Philomikros who may be 

 ignorant of the history of British agriculture. 



Although temperature may exercise little influence over the 

 distribution of Diatomacea, it may not be irrelevant to record 

 here that of the sea in the Aberdeen bay, as ascertained by 

 Mr. James Stratton, whose observations were made occasionally 

 from March 1845 to September 1846 inclusive. The mean tem- 

 perature at a mean depth of 24-5 fathoms, four miles from land, 

 is 47°*7 F., being nearly one degree higher than that of the air 

 as observed in the vicinity of Aberdeen. The minimum took 

 place in March, being 39°'5 F., exactly the mean temperature of 

 the ocean according to Sir J. C. Ross. 



