168 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Zoology). This genus will include the new species from Maine, 
which may be known as 
Macroporaster nylanderi sp. nov. 
Plate 3, fig. 7. 
Type, No. 14,966, collection of the Boston Society of Natural 
History. Collected ]:)y Olof 0. Nylander. 
Horizon and locality.— -Silurian. Found in a loose fragment 
of calcareous sandstone at New Sweden, Aroostook County, 
Maine. 
Description. — Rays short, disk large, as in other species of 
the genus. 
Infra-marginals small, nine or ten in a row, lying directly 
beneath the supra-marginals. Adambulacrals smaller than the 
infra-marginals, and throughout the greater part of the arm, 
alternating with them, so that, from the outer end of the am- 
bulacral groove to the interbrachial plate there are as many 
adambulacrals as infra-marginals, or one more. In the whole 
column there are twelve or thirteen. An extra plate is inter- 
calated near the middle of the arm in some cases, so that there 
is a small adambulacral opposite the middle of one of the infra- 
marginals. The ambulacrals are oblong plates which are not 
quite opposite, so that their line of junction is somewhat sinu- 
ous. They are deeply excavated at the line of junction between 
adjacent plates. 
The interbrachial plates are of somewhat unusual shape, the 
under surface being bent abruptly, so that while the proximal 
portion is in a horizontal plane, the outer portion forms a sort 
of tongue which projects upward at an angle of about 30° with 
the horizontal. The outline is roughly pentagonal, the inner 
sides meeting at about 90°, and each of the sides against which 
the infra-rnarginals abut, shows a re-entrant angle. The hori- 
zontal face is flat or slightly convex, while the outer one is 
rather deeply concave. The jaw-ossicles are small. 
The lower surfaces of all the adambulacrals and infra-mar- 
ginals show tubercles and some traces of spines. The inter- 
brachials appear to bear small tubercles. 
Measurements. — R, 19 mm.; r, 7 mm. 
