ANNULATA. | LOWER PALAOZOIC ARTICULATA. 131 
certainly belongs to our new genus Crossopodia, but, if correctly drawn, has much thicker and fewer feet. 
The narrow deep ¢rail of the middle part of the body on the upper surface of the planes of deposition 
of the slate, and the narrow cord-like ridge formed by the casts in them on the under surface of the 
laminze, might possibly be mistaken for a different worm resembling a Gordius, without due caution or the 
absolute demonstration of their nature, afforded by many of the specimens. 
Position and Locality Absolutely swarms in some parts of the greenish slates of Thorney Lee Quarry, 
on the Tweed, opposite Ashestiel, near Inyerleithen. 
Explanation of Figures.—P1|. 1. D. fig. 15. From the slates of Thorney Lee Quarry, on the Tweed ; 
natural size; the narrow markings being the trails left by the worms, the broader portions containing the 
body and fringe-like cirri perfect. 
3rd Ord. Tustcota. 
As their name implies, all of this order inhabit tubes, and are more or less sedentary, though not 
absolutely fixed organically to their dwelling. Their tube is either simply membraneous, formed of dried 
exudations from the surface of the body, or formed of agglutinated grains of sand, &c., or still more com- 
monly composed entirely of calcareous matter; it is usually long, open at one end and closed at the other. 
The inhabiting worms are without eyes or antennz, and have the gills attached to the sides of the 
head (whence their name Cephalobranchiata), forming two large feather-like pulsating tufts, having a con- 
tractile power sufficiently strong to drive back the blood received from the heart when it becomes aerated. 
The organs of locomotion are reduced on most of the segments to small processes, to assist in protruding 
or retracting the creature in its tube; and the cirri immediately about the head are altered into long ten- 
tacles, one on each side of the mouth, one of which in Serpula is much larger than the other, and bears 
on its extremity a circular, or conical, calcareous operculum for closing the mouth of the tube (which 
has sometimes been mistaken for Patella). 
The tube affords characters for recognizing in the fossil state the two tribes, Serpulinw and Amphitrite, 
into which the order has been divided in the recent state. 
Ist Tribe. SERPULIN &. 
Tube strong, calcareous, dull (not polished), contorted irregularly, and attached to foreign bodies. 
Marine. 
Genus. SPIRORBIS (Lam.) 
Gen. Char.—Tube discoidally coiled, of few whorls, and attached by one side of its whole length. 
SPIRORBIS TENUIS (Sov.) 
Ref.—Sow. Sil. Syst. t. 8. f. 1. and t. 11. f. 8. (8. Lewisi on plate). 
Sp. Ch.—Discoid, dextral, of one and half or nearly two whorls, partially exposed in a wide, deep, 
umbilicus ; whorls with a broad or high back, sides sloping to the umbilicus, slightly concave, bounded by 
an obtusely rounded angle on both the umbilical and outer edges; diameter rather less than one line, 
width of last whorl rather less than one-third the diameter; surface with strong transverse, and obscure 
spiral lines. 
Not uncommon, adhering to the inside of the last chamber of cephalopod shells, so that specimens 
often seem sinistral. I have only seen the surface very imperfectly preserved. 
Position and Locality—Lower Ludlow rock of Green Quarry, Leintwardine. 
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