221 



A Letter from Lewis Western Dillwyn, Esq., addressed to Sir Humphry 

 Davy, Bart. P.R.S. Read March 25. 1824. [Phil. Trans. 1824, 

 p. 413.] 



This letter is supplementary to the former one, and contains 

 further observations on the relative periods at which the different fa- 

 milies of testaceous animals appear to have been created, and on 

 the gradual approximation, which may be observed in British strata, 

 from the fossil remains of the oldest formations to the living inhabi- 

 tants of our present land and waters. 



The author observes, that the dimyairia of the strata between the 

 transition lime and lias have the ligament external, and that internal 

 ligaments were therefore confined to the monomyairia till after the 

 deposition of the Has. In the beds above the lias all the shells are 

 referrible to existing orders of animals, and it is only in the tertiary 

 beds that any of the cirrhipeda or families of naked mollusca have 

 been found. 



What is generally considered as the beak of a sepia, Mr. Dillwyn 

 refers to the cephalopode animal of an ammonite. Every shell of the 

 tertiary strata, the author observes, may be referred to some existing 

 genus ; but though this approximation has thus far proceeded in the 

 London clay, yet its numerous species are now extinct, and it is only 

 in the upper beds of crag that any fossil can be completely identified 

 with a living species. 



An Account of the Organs of Generation of the Mexican Proteus, 

 called by the Natives Axolotl. By Sir Everard Home, Bart. 

 V.P.R.S. Read June 17, 1824. [PAiY. Trans. 1824,^. 419.] 



The specimens described in this paper were taken in the month of 

 June, in a lake three miles from Mexico, at an elevation of 8000 feet 

 above the level of the sea. The usual temperature of the lake is 60, 

 and they are in such abundance as to form a principal article of food 

 of the peasantry. By the assistance of annexed drawings by Mr. 

 Bauer, Sir Everard fully describes the male and female organs of 

 these animals, and is enabled to decide that they are a full grown 

 and perfect tribe. " The attack therefore," says the author, " made 

 upon Mr. John Hunter's sagacity by Mr. Rusconi, in his work sur 

 les Amours des Salamandres Aquatiques, retorts upon himself." 



An Account of Experiments on the Velocity of Sound, made in Hol- 

 land. By Dr. G. Moll, Professor of Natural Philosophy in the 

 University of Utrecht, and Dr. A. Van Beek. Read March 18, 

 1824. [Phil. Trans. 1824, p. 424.] 



After adverting to the difference between the celerity of sound, as 

 deduced by theory and found by experiment ; and to Laplace's ex- 

 planation of the cause of that difference, and his corrections of the 

 Newtonian formula, the authors proceed to consider the influence of 



