250 Rofe—Pentremites, &c. 
Specimens of some American Pentremites (P. florealis), which 
have been cut for the sake of comparison, show a very similar struc- 
ture to P. ellipticus, with the exception that there are from four to 
six tubes connected with each row of tentacles, instead of one, as in 
that species; and those tubes are formed of a thin test folded longi- 
tudinally, so as to form a number of flat lobes or tubes, which com- 
municate with one another at the outer edge, whilst at the inner 
edge they expand into tubes, as seen in fig. 8, which is a section of 
a pair of these tubes, with the intervening lancet-plate, showing the 
connection with the pores, and removing the difficulty stated by 
M. Ferd. Roemer in his ‘Monograph on the Blastoidea,’ as it will 
be seen that the compressed longitudinal tubes shown in his Plate IV.. 
fig. 6, are really the lobes of the above-described tube. An exami- 
nation of the specimens (both vertical and horizontal sections) now 
in the British Museum will leave no doubt on this point. 
Pentremites inflatus (Phillips) and P. Waterhousei (de Koninck) 
differ from all the above, as they do not show the summit-openings, 
from which this genus derives its name; but they have one large 
circular opening at the summit of one of the quadrilateral plates, 
in the place usually occupied by the largest of those openings, and 
which is shown by Prof. Forbes to be anal. In the comparatively 
few good specimens I have been able to procure, no trace has been 
found of the pores at the base of the tentacles; but the tentacles 
appear to be inserted in a groove which forms the outer edge of the 
lobed tubes (similar to those in P. florealis above described), and 
which in these species appear to pass to the summit under the shell, 
and to open within the body, as above seen in Cyathocrinus. Neither 
the grooves nor the tentacles in these species extend quite to the 
top of the sinus. Fig.9 is a section of a pair of the tubes of P. 
inflatus, from Bolland, which resembles P. fiorealis, but has more 
lobes to the tubes. 
5. Codonaster. 
The similarity in the arrangement of the plates forming the ‘cup’ 
of this beautiful little fossil to that of some of the Crinoidea, and 
the resemblance of the rows of tentacles to those of Pentremites, 
suggested a similar organization, and led to the anticipation of find- 
ing similar pores and tubes attached to them; but on cutting many 
specimens no trace of such appendages has been found. Sections 
thus made show, however, a great similarity in the construction of 
the striations between the arms of Codonaster and those of the 
‘pectinated rhombs’ of the Cystidea. Professor M‘Coy, in the 
‘Cambridge Pal. Fossils,’ notices their external resemblance. Pro- 
fessor E. Forbes, in his ‘ Memoir on the Cystidea,’ when describing 
the ‘ pectinated rhombs,’ refers to a figure of a specimen of Echino- 
encrinus prunum, from Mr. Capewell’s collection, in which the striz 
penetrated into the substance of the body; but he was inclined to 
regard the appearance as dependent rather on some peculiarity in 
the mineralization of the specimen than on true organic arrange- 
ment. Mr. Billings, in his paper on the structure of the Cystidea, 
