STUDIES IN MARINE ECOLOGY. 



227 



temperature at the upper surface of the sand when fully exposed 

 to the afternoon sun must run much higher than the recorded 

 24. 5 C. observed for the water under these conditions. The 

 pH at Blind Gutter shows the effect of the neighboring vegetation 

 which lies on both sides of this bar. 



c. Muddy Sand Association. — The association of muddy sand 

 shades insensibly into the preceding animal community on its 

 outer side. On its inner side it includes the short eel grass 

 (Zosteria marina) which extends well out on the sand and then 

 gradually passes into the eel grass and muck association. The 

 most characteristic animal of the association is the sipunculid 

 worm, Phascolosoma gouldii and the association might well be 

 called the Phascolosoma association. Much of the muddy sand 

 may be exposed at extreme low tide. 



This community was most extensively studied at Northwest 

 Gutter, but verification studies were run at other points. Com- 

 mon animals of the association are given in list 7 but the animals 

 shown in the preceding list are also found here. 



List 7. Animals Easily Found in the Muddy Sand or 

 Phascolosoma Association. 



(See also List 6.) 



CCELENTERATA 



Hydractinia echinata, 

 Sagartia lucice. 



Annelida 



Arabella opalina, 

 Clymenella torquata, 

 Drilonereis longa, 

 Glycera americana, 



dibranchiata, 

 Lumbrinereis tenuis. 

 Nereis limbata. 

 Nereis virens, 

 Pectinaria gouldii, 

 Phascolosoma gouldii, 

 Phyllodoce catenula. 



Mollusca 



Crepidula convexa, 

 Lacuna vincta, 

 Lcevicardium mortoni 

 Littorina litorea, 

 Mya arenaria, 

 Nassa obsoleta, 

 Venus mercenaria. 



Arthropoda 



Carcinides mcenas, 

 Heteromysis formosa. 

 Libinia dubia, 

 Limulus polyphemus, 

 P alcemonetes vulgaris, 

 Virbius zostericola. 



Chordata 



Dolichoglossus. 



The analyses of water over the muddy sand association 

 (Table IX.) show an increase in range in all four factors considered 

 when compared with the conditions found on the sand bar. 

 The majority of these samples are from the edge of the short 



