. Bulletins of American paleontology. MoLLUSKs: Jackson etal. 203 Total Mollusks 1000- mean= - me(Jan-3 800- std - range-1-175 600- 400- Cd 200- v____ CO X3 CD JO - - medaii-6 . std . rangff-1-10296 • ^ Gastropods zs CO 1000- . medbn=3 O 800- etd dev-235 . range-1-175 2 600- O § 400- O 1 200- V O ^-^—_ mean-113,0 rrato>-5 raifle-1-10296 L Bivalves ^ 1000- z 800- 600- nnedtoi-2 std tanoe=1-150 400- 200- I 0 30 60 120 150 180 0 mean= 145,4 medlan=6 std dw-610,9 range-1-5727 8 10 Number of Collections Thousands of Spec
. Bulletins of American paleontology. MoLLUSKs: Jackson etal. 203 Total Mollusks 1000- mean= - me(Jan-3 800- std - range-1-175 600- 400- Cd 200- v____ CO X3 CD JO - - medaii-6 . std . rangff-1-10296 • ^ Gastropods zs CO 1000- . medbn=3 O 800- etd dev-235 . range-1-175 2 600- O § 400- O 1 200- V O ^-^—_ mean-113,0 rrato>-5 raifle-1-10296 L Bivalves ^ 1000- z 800- 600- nnedtoi-2 std tanoe=1-150 400- 200- I 0 30 60 120 150 180 0 mean= 145,4 medlan=6 std dw-610,9 range-1-5727 8 10 Number of Collections Thousands of Specimens Text-figure II.—Frequency distributions of numbers of collec- tions and numbers of specimens per genus or subgenus for total mollusks, gastropods and bivalves. Table 2.—Composition of the molluscan fauna from 24? collec- tions of fossils. Taxa Gastropoda Bivalvia Scaphopoda Cephalopoda Totals Numbers of Numbers of genera families and subgenera 89 675 54 326 7 19 1 1 149 1021 pies have not been processed for two thirds of the collections. As expected for such data (Williams, 1964; Hanski et al., 1993; Hayek and Buzas, 1997), there is a strong positive correlation between the abundance of these 156 commonest taxa, as measured by numbers of spec- imens (range 100 to 10,296), and their frequency of occurrence in the different collections (range 3 to 175) (Spearman rank-order correlation, r = , P < ; Text-fig. 12). Nevertheless, there is considerable variation in frequency. Many taxa of closely similar abundance exhibit a 5- to 10-fold range in the numbers of collections in which they occur. These differences reflect the relative eurytopy or stenotopy of taxa (Jack- son, 1974). For example, 407 VolviileUa (VolviilelUi) occur in 95 collections, whereas the scaphopod Gad- ilopsis occurs as 435 specimens in only 11 collections. Likewise, 1104 Polystira are distributed among 134 collections, whereas the next most abundant taxon Sin- cola (Sincola) is repre
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