1002 DR. J. W. GREGORY ON A NEW [Dec. 15, 
close union of the plates having 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 
echinid in the bed from which it came, 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 Lys- 
echinus belongs to an echinid fauna all the members of which are 
minute. Tiarechinus is smaller, while the species of Cidaris, 
Hypodiadema, and Salenia 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 Lysechinus as a proof that it is a larval form. 
That it is not a pathological variation cannot be so definitely 
disproved. This 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 as likely to be a post-mortem accident during fossilization as an 
ante-mortem variation. But we cannot ignore Lysechinus as a 
mere sport until we know some echinid 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 Palzozoic echinid which resembles Lysechinus 
and T%arechinus, and from which either genus can be conceived as 
having originated by a single variation. Several specimens of 
Tiarechinus are known, and they all agree in structure, so that 
that genus is not teratological ; and until we know of some echinid 
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 sutures 
is difficult. By the aid of Lovén’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 bearing 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, and they 
cannot be detected in all the areas}. 
? The sutures could probably be exposed by the application of weak acid 
but this method is not invariably successful, and so long as the specimen is 
unique it is not advisable to subject it to any risk. 
