Miscellaneous. 79 



The arms are convex above, and quite flat on the under surface ; 

 they are composed of narrow calcareous joints, each of which is 

 furnished with appendages on the inferior angles ; on the second 

 joint from the base of the arm a single short spine appears on either 

 side ; before the arm leaves the disk, the number increases to three 

 or four, the one on the inner side being longer than the others ; 

 these spines are articulated to calcareous processes, with socket de- 

 pressions for the insertion of the ball-joint of the spines ; the pro- 

 cesses are scarcely visible at first, but increase in size, until, beyond 

 the middle of the arm, their margin supplies space for the attach- 

 ment of no fewer than twelve very short spines. The inner spine gra- 

 dually increases in length from the base of the arm until it reaches 

 its maximum about 2 inches from the disk ; soon thereafter it begins 

 to decrease, and continues until it becomes of the same size as the 

 others. This long slender spine is directed inwards on the flat under- 

 side of the arm, and reaches at its greatest length fully two-thirds 

 across ; it is covered on its summit with a number of recurved 

 spikelets. The second spine is slightly compressed towards the sum- 

 mit, where, on its inner margin, it is furnished with a few spikelets 

 in a single series. When the animal is alive, a thin membrane covers 

 the whole of the spines, as in other Echinodermata ; but in dried spe- 

 cimens this is scarcely discernible. 



Two series of tentacle-pores run along the sides of the arms — one 

 pore to each joint, placed near to and in aline with the spines. They 

 can be easily traced for 2 inches or so along the length of the arm ; 

 but whether they continue much further it is difficult to say from 

 the dried specimen. Two of these pores occur at the origin of the 

 arms within the calcareous ring surrounding the mouth. 



The breadth of the body is If inch. The most perfect arm in 

 the specimen is 1 2 inches long ; but as this has been twice, perhaps 

 more frequently, broken and repaired, it is probable that its true 

 length would be at least 2 inches more. The relation of the body 

 to the arms is thus as 1 to 9. 



In the accompanying drawing (see woodcut, p. 78) the whole 

 animal is represented at about half the natural size, and the upper 

 surface of the disk at the size of life. Fig. 1 shows the under sur- 

 face of a ray about 2 inches from the disk ; fig. 2 the upper surface 

 of the same ray ; fig. 3 the under surface, towards the extremity of 

 the ray ; and fig. 4 one of the large inner spines magnified. 



MISCELLANEOUS. 



On the Pediculi infesting the different Races of Man. 



Mr. Andrew Murray, the Secretary of the Horticultural Society, 

 has lately read a paper before the Royal Society of Edinburgh on 

 this subject. He confines himself to the study of the true Pediculi, 

 including two species, viz. P. capitis and P. vestimenti, and proves 

 that the pretended P. tabescentium is oidy P. vestimenti. He ob- 

 serves, " As to colour, I find that there is a considerable difference. 

 The coloured races of man have correspondingly coloured parasites.., 



