The present paper deals with the somewhat obscure lead aluminium phosphates, of which the following varieties have hitherto been described :—

1. (i) The original plumbogummite, a mineral found at Huelgoat in Brittany, and at Nuissière, Dept. Rhône.

2. (ii) Some varieties of pyromorphite, containing alumina and water as constituents. These pyromorphites occur also at Huelgoat, and are usually quoted in books on Mineralogy as plumbogummite, although Damour, in his original paper on the subject, clearly distinguishes between the true plumbogummite and the aluminous pyromorphites.

3. (iii) The American mineral, bitehcockite, occurring in the Canton Mines, Georgia.

4. (iv) A Cumberland mineral, which for some time was mistaken for zinc silicate, but has recently been shown to be a phosphate of lead and aluminium (Miers, Min. Mag. 1896, XI, 272).