ORGANIC DEPENDENCE AND DISEASE 
99 
Fig. 84. Caulostrepsis taeniola growing in the shell of the brachiopod Stropheo- 
donta from the Coblentzian (Lower Devonian) of Seifen. The margins of the 
brachiopod valves have been entered on all sides simultaneously by these borers 
which have made loop-shaped tubes joined by a median cavity. Together with 
these are simple tubes of Palaeosabella. 
of tlieir entrance. Often the tubes adapt themselves to the 
thickening or thinning valves, taking advantage of the for- 
mer to recurve or loop, and compelled by the latter to flatten 
down. The tendency to make a hook or loop, or to take on 
the U-shape, is shown in many cases and the development 
of a clavate form at the blind end is frequent and charac- 
teristic. Most interesting beyond these features is the fact 
Fig. 85. Cast of poucli-shaped (algal?) borings extending in from the surface of 
a brachiopod shell, x 4. Oriskany sandstone (Lower Devonian). 
