REPORT OF THE DIRECTOR 1920-21 183 



same thing. Some of the oysters in this bed are of very large size, 

 but the majority of the shells belong to young forms, and there are 

 a large number of very young forms, " baby " oysters. Also asso- 

 ciated with the oyster shells are a number of other marine species 

 of shells : Mya arenaria Linn., Modiola demissus 

 (Dill.), Mulinia lateralis (Say), and Alectrion 

 (Nassa) obsoleta (Say) . Balanus crenatus Brag, 

 was collected here; but as that form occurs on the oyster shells, 

 it is of no importance in this connection. I have discussed this 

 bed of shells found at Croton Point with the State Archeologist, 

 Arthur C. Parker, and he believes that the conditions found there 

 warrant the assumption that the occurrence is an oyster bed. 



Of the marine forms collected at Croton Point, all but the oysters 

 are in too small numbers or too fragmentary to make comparisons 

 as to size with typical marine forms. Mulinia lateralis we 

 have discussed above as larger than the specimens from Storm 

 King and smaller than the recent shore forms. The oysters occur 

 in very large sizes and the largest specimens are quite massive; but 

 this is a euryhaline form which thrives in water with diminished 

 salt content (Walther, 1920, p. 210). 



A number of fresh-water gastropods were found to be of rather 

 frequent occurrence in the oyster beds. They are Polygyra' 

 h i r s u t a (Say) , Polygyra fraudulenta (Pilsbry), 

 Eyrgomphala alternata (Say) and Planorbis sp?. 

 These species undoubtedly were carried in by streams. 



Ries (p. 594, pi. 14) reports sponge spicules from Croton Point; 

 also five species of fresh-water diatoms. At Croton landing a number 

 of impressions were found in the blue clay which were identified as 

 worm tracks by Professor Hall. 



The Pleistocene fauna of the Hudson valley; as far as present 

 knowledge goes, is very small; but I am of the belief that, with this 

 problem in mind, more information can be obtained through further 

 work along these lines. The present evidence, however, seems to 

 lead to the same conclusions as were drawn for the Champlain 

 area. The waters of the Pleistocene Hudson estuary were so 

 freshened in going northward that (1) only a few marine forms were 

 able to advance into these waters at all ; (2) so far as present knowledge 

 goes, only two species reached as far up as Storm King, 50 miles above 

 New York, and none has been reported north of this locality; (3) the 

 two species found at Storm King represent a dwarf fauna, one of 

 them, Mulinia lateralis, occurring in a dwarfed condition 

 (less so, however). at Croton Point about 20 miles farther south. 



