296 Miscellaneous. 



Measurements of the Trunk of the Aurochs. 



Inches. 



Length of vertebral column from the atlas to the sixth caudal 



vertebra, measured across the diapophyses 81 



Length of vertebral column over the neural spines 88 



Length of cervical region over the diapophyses 17 



Length of dorsal region ditto 30 



Length of lumbar region ditto 13 



Length of sacral and six caudal ditto 21 



Depth of spine of seventh cervical 8 



Depth of spine of first, second and third dorsal, being the 



three longest, each 11 



Length of first rib 9 



Length of ninth, or the longest 18^ 



Seven ribs articulate by separate haemapophyses to the sternum. 

 Length of diapophysis of fourth lumbar, or the longest . . 4^ 



Breadth of atlas across the neural arch 7 



Extreme breadth across the spines of the ilia 14 



Extreme breadth across the pubis, from the inner edge of 

 each acetabulum 6 



MISCELLANEOUS. 

 On the Velvet-like Periostraca q/Trigona. By J. E. Gray, Esq. 



In my account of the species of the genus Trigona of Megerle, I 

 mentioned that several species were covered with a velvet-like 

 silvery coat hiding the surface of the horny periostraca. 



When this coat is minutely examined, it is found to be formed of 

 numerous elongated spicula of a uniform length placed side by side 

 perpendicular to the surface of the periostraca, so as to form a pile 

 like velvet or plush. The length of the spicula, and consequently 

 the thickness of the coat, increases towards the margin of the shell. 

 This coat is generally rubbed off from the more convex part of the 

 specimens which have not been very carefully preserved, but in such 

 examples it is usually to be found near the edge of the valves, or on 

 the lunule and other sunken portions of the surface. 



The Rev. Dr. Fleming has lately drawn my attention to the fact, 

 that these spicula are siliceous and s^imilar to those of siliceous 

 sponges ; indeed Dr. Fleming is inclined to regard the velvet-like coat 

 as a species of Halichondria parasitic on the shell rather than as a 

 portion of the periostraca itself ; and Dr. George Johnson of Ber- 

 wick, who examined Dr. Fleming's specimen with me, is inclined to 

 take the same view of the question. 



With these authorities opposed to my view I have reconsidered 

 the question, but I am still inchned to believe that I am correct in 

 considering the spicula as part of the shell formed by the animal as 

 it produces the periostraca on the edge of the shell, and offer the 

 following reasons in support of this conclusion : — 



1st. This kind of coat is found on several species of the genus 

 which inhabit different pa>rts of the world. 



