1889-90-] On the Ecliinoidea or Sea- Urchins. 355 



well rewarded for the trouble. In a few slides which I sent 

 to Mr AVilliam Penman, F.R.M.S., for examination, he has 

 identified species belonging to the following genera of the 

 Diatomaceae: (1) Pleurosigma ; (2) Ehabdonema ; (3) Coscino- 

 discus ; (4) Melosira ; and (5) Heliopelta. These were all found 

 among a few particles of sand taken at random from the interior 

 of a spatangus shell, so that a more careful inspection would 

 no doubt result in the discovery of many others. 



The species of sea-urcliins found in tropical seas are both 

 numerous and varied in form, while many are extremely 

 beautiful. The splendid collection of the Echinoidea brought 

 home by the Challenger, and now described by Prof. A. 

 Agassiz in the third volume of the " Challenger Pieports," 

 includes no fewer than forty-nine deep-sea species hitherto 

 unknown to science. The wonderful diversity in their 

 appearance strikes one very forcibly in looking over the 

 numerous plates appended to the volume. The same remark- 

 able diversity, indeed, may be seen in any good museum 

 collection. I have had the good fortune to receive from a 

 friend in Australia, lately a member of this Society, a specimen 

 of what is certainly one of the most curious forms amongst 

 the sea-urchins. In this species the spines have decreased 

 in number, and the primary spines have become much 

 thickened and lengthened, while their colour is frequently a 

 pale brown, lightened up with red at the extremities. This 

 singular appearance of the spines has suggested the name by 

 which the animal is locally known of " cigar-fish." The 

 specimen now shown was captured by my friend on Lady 

 Elliot Island, and afterwards taken to the Curator of the 

 Natural History Museum at Brisbane, who pronounced it to 

 be Heterocentrotus mamillatus of Brandt, and the largest 

 specimen of it he had ever seen. Professor A. Agassiz, in his 

 ' Pievision of the Echini,' gives as many as fifteen synonyms 

 for this species, so that it must have proved somewhat of a 

 puzzle to the classifiers. The " cigar-fish " is a native of the 

 Eed Sea, and of the Sandwich, Fiji, Philippine, and other 

 islands. 



Several species of the Echinoidea were well known to the 

 ancients, being mentioned by Horace, Martial, Aristophanes, and 



