1892] MARYLAND ACADEMY OF SCIENCES. 225 



the one now in use, four feet beneath the water. I also 

 examined the piles of the old wharf at Split Rock (be- 

 tween Potomac and Aquia creeks), Virginia. Here I was 

 not able to Und a single specimen. I thought it might be 

 due to the fact that the channel of the Potomac in this 

 region lies well toward the Maryland side, being separated 

 from this old landing by flats two miles in breadth. Col- 

 onies thus widely separated from the course of the larger 

 vessels, when once destroyed, which at this exposed point 

 might easily happen, would not quickly become re-estab- 

 lished. The hydroids may have been absent from some 

 unknown cause at this particular season (cf. p. 220), but this 

 is rendered improbable by the fact that on the following day 

 I crossed the Potomac to Clifton Beach, and there found 

 flourishing colonies on the older piles of the landing. The 

 most northerly point in the Potomac at which they were 

 found was Fort Washington, Maryland. On the same day 

 that I saw them there, I examined the docks at Alexandria, 

 Virginia, which is about six miles further up stream, with 

 a negative result. 



Judging from what I have seen of the tide-water of the 

 Rappahannock, I should not expect to find Cordyl- 

 ophora farther up this estuary than Port Royal, and I 

 should confidently look for it at Tappahannock. The 

 tide-water at Fredericksburg, as recently observed in 

 passing over the Aquia Creek and Fredericksburg railroad 

 bridge, appears, like that of the James at Richmond, to 

 bear too much sediment for the health of the , colonies. 



Early in the present month my brother and myself 

 found Cordylophora growing in abundance on the supports 

 of the docks in the York at West Point, Virginia. Here the 

 saltness of the tide-water is very decided, and near at 

 hand are the well-known York River salt-water oyster beds- 

 The occurrence of the colonies so near the mouth of the 

 Bay was a matter of considerable surprise to me, for I have 



