VVIGLEY and STINTON: REMAINS FROM MARINE SEDIMENTS 



ruary-March to 14°C in September-November. 

 Temperatures of inshore surface waters sub- 

 stantially exceed these values, 



Nontidal movements of water masses on the 

 continental shelf within the area are generally 

 westward. Water in the Gulf of Maine and 

 Nantucket Sound tends to flow southwesterly 

 across Nantucket Shoals and into the area. Con- 

 versely, surface waters offshore beyond the 

 continental shelf flow easterly. Authors who 

 have published further information on the hy- 

 drography of the area include Bigelow (1927, 

 1933), Bumpus and Day (1957), Bumpus et al 

 (1957), Day (1958), and Colton (1964, 1968, 

 1969). 



ORDER OF DISCUSSION 



The most common animal remains in the sam- 

 ples studied were echinoderms, mollusks, and 

 fish. Considerably less common than the fore- 

 going were remains of crustaceans and coelen- 

 terates. The order in which these groups are 

 discussed below is according to the abundance 

 of remains in each major group, namely, echi- 

 noderms, mollusks, fish, and crustaceans and coe- 

 lenterates. 



REMAINS OF ECHINODERMS 



Echinoderms were the most numerous and 

 quantitatively dominant group of animal re- 

 mains occurring in the area. The sole contrib- 

 utors in this group were the echinoids. Spines 

 and test fragments were rare to very abundant 

 and were widely distributed. Presumably the 

 skeletal fragments of asteroids and ophiuroids, 

 of which living members of both groups are 

 common in this region, were generally too small 

 to be recovered using the 1-mm mesh screen. 

 Of all macroscopic animals in the samples, the 

 common sand dollar, Echinarachnius parma 

 (discussed in the following subsection), was by 

 far the leading component. Spines were the 

 principal structures recovered from heart ur- 

 chins and sea urchins. Some examples of typical 

 echinoderm remains are illustrated in Figure 3. 



The size of fragments of most organisms dis- 

 cussed in this section ranged from 1 mm (sand 



size) to 1 cm or more. The largest remains 

 were tests of whole or nearly whole E. pai-ma. 

 Adult size of living members of this species 

 (about 7 cm) is less than some of the other non- 

 molluskan species, but the comparatively strong, 

 compact test is much more resistant to fracture. 

 This durability, plus the enormous supply in the 

 form of living individuals, contributed to the 

 abundance of fragments of this species in the 

 sediments. Counting the E. parma and other 

 echinoids was impractical owing to the enormous 

 numbers of small fragments, plus a gradation 

 in size that precluded the separation of major 

 fractions from minor ones. Occurrence of 

 Brisaster fragilis, Echinarachnius parma, and 

 Strongylocentrotus drobachiensis are listed by 

 stations in Table 2. 



ECHINARACHNIUS PARMA 



Remains of E. parma were widespread (Table 

 2) and numerous. This species ranked first in 

 volume and number of fragments of all organic 

 remains in the study area; it occurred at 73 Cr 

 of the stations. It was most abundant in the 

 vicinity of Nantucket Shoals (stations 2, 3, and 

 16). E. parma fragments made up nearly 30^ 

 (by volume) of the substrate near station 3. In 

 deepwater areas in the vicinity of the middle and 

 outer shelf, the density of fragments was low — 

 occasionally less than 50/m= or about 0.01 '"r by 

 volume. (All animal remains combined gener- 

 ally formed less than 1% by volume of the sub- 

 strates of the outer shelf and slope.) 



The distribution of E. parma extended from 

 the shallow inshore areas across the entire shelf 

 to the upper portion of the continental slope 

 (Figure 4). Surprisingly, it was rather sparse 

 near the middle of the shelf. Fragments from 

 inshore areas were diff'erent in size, color, and 

 sphericity from those collected oflfshore. Test 

 fragments from the inshore zone, which extends 

 out to 50 or 70 m, were whitish, usually larger 

 than 5 mm in greatest dimension, and had sharp 

 and angular edges and apexes (Figure 3A). 

 Fragments from depths of about 80 m or more 

 were greenish-brown, commonly less than 5 mm 

 long, and had rounded edges. In contrast to the 

 fresh, new appearance of the test fragments 



