The majority of the lots analyzed were obtained by 15 

 research vessels; a small percentage of the lots did not have a 

 vessel designated or were obtained by hand sampling along 

 the shore, scuba diving, or other means. Among the collecting 

 vessels were: Fish Hawk, Gilbert, Harengus, Albatross III, 

 Delaware I, Delaware 11. Albatross IV, and Blueback, all 

 operated by the National Marine Fisheries Service (NMFS), 

 or its predecessor agencies the Bureau of Commercial Fisher- 

 ies (BCF) and the U.S. Fish Commission (USFC). There were 

 four commercial fishing vessels chartered by BCF for re- 

 search purposes: Whaling City, Shirley and Roland. Silver 

 Mink, and Priscilla V. The A. E. Verrill. operated by the 

 Marine Biological Laboratory (MBL). Woods Hole, Mass., 

 and the Gosnold and Asterias of the Woods Hole Oceano- 

 graphic Institution (WHOI), Woods Hole, Mass., also pro- 

 vided collections included in this report. Table 1 lists the 

 pertinent sampling statistics for each vessel. Data pertaining 

 to each lot of bivalves in the NEFC Specimen Reference 

 Collection are contained in Theroux and Wigley 4 ; information 

 for each group includes: vessel name, cruise number, station 

 number, type of sampling gear, latitude, longitude, sampling 

 date, water depth in meters, and bottom type. 



Bathymetry 



Water depths, in meters, were obtained by means of depth 

 sounders at sea and from published navigation charts or 

 bathythermographic records where actual depth soundings 

 were not available at time of sampling or for inshore collec- 

 tions. For ease of processing and to facilitate discussion of 

 distribution with depth, depths were grouped into eight depth 

 range categories. Range groupings used are: 1 ) 0-24m, 2) 25-49 

 m, 3) 50-99 m. 4) 100-199 m, 5) 200-499 m, 6) 500-999 m, 7) 

 1,000-1,999 m, and 8) 2,000-3,999 m. 



Geology 



Data for the majority of the samples contained information 

 on 34 different types of bottom sediments. Considering the 

 areal scope of this report, and the restrictions on legibility 

 enjoined by the amount of reduction required to the base 

 charts, we have grouped the 34 more detailed sediment types 

 into 2 separate, more generalized, subgroups. The first sub- 

 group used in the tables accompanying the taxon/sediment 

 relations discussion, contains nine sediment categories: 1) 

 gravel, 2) sand-gravel, 3) till, 4) shell, 5) sand-shell. 6) sand, 7) 

 silty sand, 8) silt, and 9) clay. The second subgroup, used in 

 the sediment distribution chart (Fig. 2). groups the above nine 

 categories into four, more general, classes for ease of inter- 

 pretation on the chart: thus, in the chart, sediment types are: 

 1) gravel, 2) shell, 3) sand, and 4) silt-clay. 



Sampling Gear 



A total of 28 different sampling devices were used in obtain- 

 ing the bivalves in the NEFC collection. Among the devices 



■Theroux. R. B..andR. L. Wigley. 1979. Collection data for U.S. east coast 

 bivalve mollusks in the Northeast Fisheries Center Specimen Reference Col- 

 lection Woods Hole. Massachusetts. Unpubl. manuscr.. 471 p. Northeast 

 Fisheries Center Woods Hole Laboratory. National Marine Fisheries Service. 

 NOAA. Woods Hole. MA 02543. 



are a variety of grab samplers, dredges, and trawls, various 

 nets, and skimmers; in addition scuba divers, and hand col- 

 lecting yielded specimens, and some were obtained from fish 

 stomachs. Table 2 lists the various types of sampling gear 

 used and the number and percent samples for each type. 



Data Treatment 



Original samples were preserved in buffered formaldehyde 

 solution at sea and subsequently transfered to alcohol pre- 

 servative when sorted in the laboratory. All information per- 

 taining to these collections has been stored on magnetic tape 

 at the NEFC. 



Whenever possible an attempt was made to arrive at a 

 determination at the species level for all lots examined: 

 however, time and personnel constraints as well as damaged 

 specimens necessitated the use of higher taxonomic levels in 

 some cases. Consequently this report contains determina- 

 tions at the familial and generic levels as well as those to the 

 specific level. 



BOTTOM SEDIMENTS 



The following discussion on the distribution of bottom sedi- 

 ments over the entire sampling area is based on the informa- 

 tion contained in Figure 2. 



The predominant sediments in the study area are of the 

 sandy and muddy (silt-clay) types. Sandy substrates occupy 

 nearly the whole of the continental shelf and nearshore re- 

 gions from Georges Bank to Key West, Fla. Muddy sub- 

 strates predominate on the outer continental shelf and slope, 

 in many of the embay ments, and in the deeper basins of the 

 Gulf of Maine. 



Gravelly substrates are quite widely distributed primarily 

 in the Gulf of Maine and are patchily distributed on the 

 Southern New England shelf and in the Mid-Atlantic Bight 

 region between Cape Cod and Cape Hatteras, becoming 

 almost nonexistent below Cape Hatteras. No gravelly sub- 

 strates occur south of Myrtle Beach, S.C. 



Shelly substrates occur predominantly on the continental 

 shelf south of Cape Fear, N.C., and in some nearshore areas 

 in rather discrete patches. Two of these small patches of 

 shelly sediments were also encountered along the northeast- 

 ern coast of Maine and south of Grand Manan Island. 



DISTRIBUTION OF CLASS BIVALVIA 



The areal distribution of samples with regard to water depth 

 is shown in Figure 1. 



Occurrence frequency of samples in the various water 

 depth ranges shows a decided affinity for the midcontinental 

 shelf depths. Fully one-third (33.6%) of the samples are from 

 water depths of 50 to 99 m gradually diminishing in frequency 

 with both increasing and decreasing water depth range. 



The number of bivalve specimens was significantly highest 

 (41%) in the 50-99 m depth range grouping; about equal (17 

 and 16%) in the shallower depth range groupings, 0-24 and 

 25-49 m, as well as the 100- 199 m grouping ( 16%); and gradual- 

 ly decreased with increasing depth range beyond 200 m. Table 

 3 lists the occurrence of bivalve samples and specimens in 

 relation to range in water depth. 



