THE ECHINODERMS OF THE WOODS HOLE REGION. 
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1. Arbacia punctulata (Lamarck). Common sea-urchin. (PI. 7, tigs. 48-52.) 
Echinus punctulatus, Lamarck, 1816. 
Arbacia punctulata, Gray, 1835. 
Echinocidaris davisii, Agassiz, 1863: Verrill, 1866. 
Description. — Diameter of test 30 to 50 mm.; height 15 to 25 mm. I) =2 II. more or less. Length of 
longest spines 20 to 25 mm. ; diameter of anal system 4 to 6 mm. ; diameter of whole abactinal system 
10 to 15 mm. ; diameter of peristome 15 to 25 mm. Test somewhat flattened, sloping markedly toward 
ambitus, which is nearly circular; actinal surface flat, the peristome only slightly sunken. Branchial 
incisions deep, with prominent everted edges. Anal plates normally 4, occasionally 3 or 5. Ocular 
plates (radials) excluded from the circumanal ring in young specimens, but in old ones 1 or 2 sometimes 
enter it slightly. Genital plates (basals) large, the madrepore plate evidently largest. Ambulacra 
straight, narrow above the ambitus, but wider below. Poriferous zones narrow, with large pores, in 
simple pairs dorsally, then in arcs of 3, and on the very edge of the peristome polyserial. Spines few 
near the abactinal system, the upper half of the median interambulaeral space being entirely free from 
them; secondary and miliary spines altogether wanting; primaries longitudinally striated, longestat am- 
bitus, shortest near abactinal system; those above ambitus pointed or blunt; those at ambitus and below 
flattened and more or less rounded at tip, and often with a median longitudinal ridge there; those 
nearest peristome shorter and more or less spatulate. Primary tubercles smooth, imperforate, in a 
double series on each ambulacrum; in 4 to 8 or more series on each interambulacrum, of which the 
2 middle series are smallest, with only 4 or 5 small tubercles each, while the outermost are as long 
as the ambulacral series. Transverse rows of interambulaeral tubercles oblique. All tubercles, 
diminish in size from ambitus upward. A specimen with D=36 mm., 11=18 mm., has 13 coronal 
plates. Buccal plates, 5 pairs, prominent. Color in life, reddish or purplish brown of some shade' 
varying from a light dull reddish to almost black; tube feet, brownish red. 
Range. — Nantucket Shoals and Woods Hole to west Florida and Y ucatan ; low water to 125 fathoms. 
Remarks. — This is the common sea-urchin of the Woods Hole region. It' is abundant at many 
places in Vineyard Sound, and is common in Hadley Harbor and, at times, around the Fish Commis- 
sion wharf. We took one specimen off Sankaty Head, but none at Crab Ledge. In spite of its 
abundance, we know little of its habits, and its development-is only partially known. Carman and 
Colton (’82) have published some notes on the development, and Fewkes (’81) has also contributed 
to our knowledge of the early stages. 
2. Strongylocentrotus drobachiensis (0. F. Muller). Green sea-urchin. (PL 9, tigs. 53-57.) 
Echinus drobachiensis O. P. Muller, 1776. 
Echinus neglectus Lamarck , 1816. 
Echinus grdnularis Say, 1827. 
Strongylocentrotus chlorocentrotus Brandt, 1835. 
Echinus granulatus Gould.1841. Desor, 1848. 
Toxopneustes drobachiensis Agassiz, 1846. 
Eurycchinus granulatus Verrill, 1866. 
Euryechinus drobachiensis Verrill, 1866. 
Strongylocentrotus drobachiensis A1 . Agassiz, 1872. 
Description. — Diameter of test 60 toSOmm.; height 25 to 45 mm. ; D = 1.75 to 2.25 IP. Length of 
longest spines 10 to 14 mm.; diameter of anal system 6 to 8 nun. ; diameter of whole abactinal system 
15 to 20 mm. ; diameter of peristome 18 to 25 mm. , very much larger in proportion in' young specimens, 
sometimes 60 per cent of the diameter. Test more or less flattened, curving at first very slightly then 
abruptly to the circular ambitus, actinal surface flattened, the peristome sunken 4 to 6 mm. Branchial 
incisions rather small, and not very deep. Anal plates at first 2 or 3, but increasing in number 
with age, adults having 35 to 40. Ocular plates (radials) large, two entering circumanal ring to a 
marked degree. Genital plates (basals) very large, the madrepore much the largest. All the plates 
of the abactinal system carry miliaries, though they are few on the madrepore. Ambulacra broad at 
the ambitus, narrower at the peristome, though there they are much wider than interambulacra. 
Poriferous zones broad, with numerous small pores; pairs of pores in oblique transverse series, 
abruptly bent at outer end; number of pairs in each series varies somewhat with age, but is usually 
from 4 to 6; obliquity of series varies much with age, in very small specimens approaching the 
vertical — in old specimens more nearly horizontal, Spines numerous all over the test; primaries 
longitudinally striated, pointed but not very sharp, longest at and. above ambitus, shortest around. 
