— 329 — 
median series or two inner lateral series—though the former condition 
is most probable —I have not been able to determine definitely. 
AS Seeley states regarding the abdominal ribs of M. tenuidens, «they 
are five or six times as. numerous as the costal ribs», and I believe 
are more numerous than in Stereosternum, and perhaps somewhat 
heavier. 
In none of the specimen studied ‘is ‘there any indication of bony 
scutes or any sort of dermal armature, and I believe the skin was 
protected only by very minute horny epidermal scales, or else was 
naked like the more protected parts of the skin in many of the 
Testudinata. A few of the bones show a finely wrinkled surface, 
certainly not'a natural bone surface, which may be the imprint of a 
delicate integument. In this connection it is ‘of interest to note the 
recent observations of M. Leon Vaillant (1903), who has reéxamined 
Gervais’ original specimens. Vaillant believes that a small oval ‘body 
figured in Gervais’ plate and by him regarded as a foreign object, - —_— 
probably ' a trilobite, — represents a portion of the skin from the 
ventral surface of the body, covered with trapezoidal scales resembling 
the ventral scales of certain snakes, If Vaillant’s interpretation is 
correct, it is certainly remarkable that no other specimen shows 
the slightest indication of dermal or epidermal scales. One example 
of Stereosternum which I examined shows the outline of the 
soft parts quite clearly, but yields no evidence of the presence of 
scutes. 
