1002 DB. J. y/. GEBGOEY ON A NEW [DeC. 15, 



close union of tlie plates Laving obscured the sutures, and to 

 irregularity in the normal symmetry. 



The small size of the specimen at once raises the question as to 

 whether it is mature or is only a form so young that it is useless 

 to found a genus upon it. If the specimen were the only 

 eehinid in the bed from which it camo, or had been associated 

 with echinids of normal size, it would probably have been im- 

 possible to give a satisfactory reply to this objection. But Lt/s- 

 ecJihiiis belongs to an eehinid fauna all the members of which are 

 minute. TiarecMnus is smaller, while the species of Ciclaris, 

 Hypodiadema, and Salenta are of about the same size. The 

 specimens of the last three genera have the characters of maturity, 

 in spite of their minuteness, and thus we cannot take the small 

 size of Lysechhius as a proof that it is a larval form. 



That it is not a pathological variation cannot be so definitely 

 disproved. Tliis idea seems supported by the fact that the radial 

 symmetry of the specimen is not perfect. One of the inter- 

 ambulacra is more prominent than the rest, but this malformation 

 is aa likely to be a post-mortem accident during fosailization as an 

 ante-mortem variation. But we cannot ignore Lysechinus as a 

 mere sport until we know some eehinid which may be regarded 

 as the form of which it is the sport. Numerous echinids are 

 known with some striking character which may be explained by 

 teratology ; but in such cases there is no doubt as to the species, 

 or at least the genus, from which the sport arose. There is no 

 known Triassic or Palaeozoic eehinid which resembles Lysecldnus 

 and Tiarechimis, and from which either genus can be conceived as 

 having originated by a single variation. Several specimens of 

 2'iarcchinus are known, and they all agree in structure, so that 

 that genus is not teratological ; and until we know of some eehinid 

 from which Lysechinus could have sprung we cannot adopt the 

 easy course of dismissing it as an abortion. 



The greatest difficulty presented by the specimen is due to the 

 close union of the plate, whereby the recognition of the eutm-ea 

 is difficult. By the aid of Loven's fluid I believe that I can see 

 sutures which show that each interambulacrum consists of nine 

 plates, arranged as follows : — 



1. Adjoining the genital plate are three quadrangular plates. 



2. Three quadrangular plates, each beai-ing a tubercle. 



3. Two angular plates, each bearing a tubercle. 



4. One peristomal plate. 



This arrangement is not altogether free from doubt, for it is 

 difficult to discriminate between cracks and sutures, aud they 

 cannot be detected in all the areas '. 



' The Buturea could piobubly be exposed by the application of weak acid 

 but this method is not invariably bucccbbCuI, and bo long us the specimen ie 

 unique it is not advisable to subject it to any risk. 



