158 NEW YORK STATE MUSEUM 



Taken as a whole this combination is ver}^ comphcated commen- 

 saHsm from a date so ancient as the Devonic, more extreme than 

 any other yet known from the Paleozoic rocks. - But we find a 

 somewhat parallel case in the present described by Bouvier as occur- 

 ring in the Gulf of Aden — a coral and a worm growing together, 

 and hidden in the coral substance a gastropod on which both settled 

 down when the partnership began ; furthermore there appears to be 

 a small bivalve in association with the worm. Other somewhat 

 similar cases might be cited. 



The Devonic coral Acervularia and the spiral worm Streptindytes 

 acervulariae ; a Siluric Stromatopora with a somewhat similar spiral 

 worm, Streptindytes concoenatus; a Devonic Stromatopora with 

 the spiral worm, Streptindytes compactus. The first of these occur- 

 rences was described some years ago by Prof. Samuel Calvin [On 

 a New Genus and Species of Tubicolar Annelida. Am. Geol. 1:24. 

 1888]. It is the case of a large annelid whose tube measures J to 

 J inch in diameter growing upward in numbers among the cells of 

 the compound coral Acervularia davidsoni Edw. & H. from 

 the Middle Devonic rocks of Iowa. The species has not before been 

 illustrated and I have to thank Dr Calvin for the privilege of 

 introducing the accompanying cut of this interesting commensal 

 [pi. I, fig. 7]. 



Another example of these spiral commensal worms (Streptin- 

 dytes concoenatus) is afforded by the Stromatopora reefs 

 of the Cobleskill limestone (Upper Siluric). The illustration here 

 given [pi. I, fig. 5, 6], affords some idea of how a small mass of Stro- 

 matopora may be quite riddled with these minute corkscrews. 

 This is taken from a single section across a small colony in which it 

 is apparent that these worms have become sessile at different stages 

 of growth in the coral mass as they start at different levels in the 

 colony. It is also clear that the worm tube made at least one hor- 

 izontal convolution before starting on its upward spiral growth and 

 it is more than likely that its elongated spiral is due to the require- 

 ment of keeping its tentacular end up at the feeding surface of the 

 growing coral. These tubicolous worms have very plastic tubes and 

 readily adjust themselves to surroundings. In the worm of Pleu- 

 rodictyum (Hicetes innexus) the early spiral form was 

 soon lost, perhaps because the coralHtes are so large and close that 

 such growth wns eff'ectualiy obstructed, I have given here some 



