398 W. KEEPING ON THE DISCOVERY OF MELONITES IN BRITAIN. 



The British-Museum specimen is smaller (4 inches by 3 inches) ; 

 but it is a fragment of probably quite as large an individual, as we 

 see from the size of its plates. 



On one side the test has been much disturbed, the whole surface 

 being covered with a confused mass of interambulacral plates and 

 a few ambulacrals ; but on the other surface we have a well-preserved 

 interambulacral area composed of five or six ranges of plates, an 

 extra range being intercalated between the others as we approach 

 the equator. The outer edges of the bordering ranges are bevelled 

 off, showing that they were overlapped by the ambulacral plates ; 

 these latter are seen confusedly heaped together in two masses bor- 

 dering the interambulacral area on either side. 



The tubercles and spines are well preserved. 



It is remarkable that whereas in the larger specimen the ambula- 

 cral areas are preserved with their plates in position amid the 

 scattered plates of the interambulacral system, here it is the ambu- 

 lacral ranges that have given way, while the interambulacrals still 

 preserve their natural relations. 



Melonites Etheridgii, n. sp. 



Specific Characters. — Test large (diameter of crushed specimen 7 j 

 inches), spheroidal (?), composed of very thick plates arranged in 

 five ambulacral and five interambulacral areas. All the plates 

 ornamented with minute tubercles for the support of the spines. 



Interambulacral areas broader than (twice as broad as?) the 

 ambulacrals, composed of numerous (nine?) ranges of plates, 

 marginal ranges pentagonal, the rest hexagonal, articulating with 

 each other by faces which vary from a right angle to one of thirty 

 degrees with the exposed surface. Ambulacral areas large (1| inch 

 wide), each consisting of two broad ribs separated by a slight de- 

 pression along its median line running from mouth to anus ; com- 

 posed of numerous (twelve to fourteen) ranges of irregular plates, 

 each perforated by a pair of simple pores on its outer margin. 



Tubercles minute, imperforate, without boss, of two orders, the 

 larger kind surrounded by a smooth areola, bounded by an elevated 

 ring. 



Spines small (length 3-6 millims.), tapering, coarsely sulcate, 

 with a prominent collar round the articular end. 



Affinities and Differences. — The only forms which require a close 

 comparison with our fossil belong to the genera Melonites and Oligo- 

 joorus of the group Perischoechinidse ; with these it agrees in the 

 thickness of its test, its numerous ambulacral and interambulacral 

 plates, and in the absence of large tubercles; but Oligoporus has 

 not more than four ranges of plates in its ambulacral areas. 



As a species, this is well distinguished from Melonites multiporus, 

 "N. & 0., by the characters of its ambulacral areas : these are com- 

 posed of twelve or fourteen ranges of plates separated into two zones 

 by a median depression, and the two middle ranges are not larger than 

 the others ; in M. midtiporus, N. & 0., they are composed of eight 



