Eider Duck on the Ylhan. 635 



contribution, fig. 128 giving the beak of a typical Shear- 

 water, <ind figs. 139 & 130 those of Petrels of the genus 

 JEstrelata. I am of opinion that JS. vociferans was closely 

 related to J^. caribbaa (fig. 129), as I have attempted to 

 show upon a previous page of the memoir. 



"The differences in tiie osseous mandibles of a Petrel 

 (jEsirelata vociferans) and a Shearwater [Pvffinus Iher- 

 minieri) are easily appreciated upon comparing those parts 

 iu figs. 5 & 6 of pi. i. All Petrels and petrel-like birds 

 possess osseous beaks or mandibles, such as we find figured 

 in figs. 1-5, pi. i. ; in fig. 11 of pi. iii., as well as in Cook's 

 and the Diving Petrels. 



" The tarso-metatarsus is generally long and slender in the 

 Petrel-like forms ; shorter and stouter in the Shearwaters. 

 (See the various figures of this bone on my plates.) 



" The ' Cahow,' then, was a Petrel of the genus /Estrelata; 

 and with this point settled, I can proceed to give an account 

 of its skeleton.''* 



A full account of its osteology here follows in my memoir, 

 which some day will doubtless be published. 



EXPLANATION OF PLATE XX. 



Upper figure : The entrance to Crystal Cave, Bermuda. 



Lower figure : Mr. Mowbray at work in the interior of Crystal Cave. 



XXXI.— £/V/e>' Buck on the Ythan. 

 By Brig.-General H. R. Kelh, M.Ham.O.U. 



The river Ythan flows into the North Sea between 

 Aberdeen and Peterhead. The coast there is very wild. 

 Along the shores are sandhills, bordered inland by stretches 

 of rough heather — a country very interesting to the natu- 

 ralist, as it teems with bird-life. 



In the spring months the chief feature of the Ythan 

 Estuary is the enormous number of Eider Duck : hundreds 

 of them, male and female, congregated on the sands or 



