158 
PALEONTOLOGY OF NEW YORK. 
Fig. 151. 
Thence they bend inward and of catazyga neadi, Biiiings; 
showing the form of the spiral cones 
(Lorraine) shales of central New York, that is, the pedicle-cavity is deep, and in 
front of it lies a more deeply excavated, short, sharply defined and longitudinally 
striated impression. In the brachial valve is a broad anterior and a narrow, elon¬ 
gate posterior pair of scars. The spirals are of essentially the same character as 
in Z. modesta, though the form of the cones is such that their apices converge 
toward the median line in a plane just below the surface of the brachial valve. 
The loop, however, differs; in the first place, it is 
persistently posterior in its position, originating as 
in Atkypa, the lateral lamellae bending downward 
toward the bottom of the brachial valve and 
directed forward in lines which are parallel for a 
short distance. 
upward, meeting in a sharp angle in the space just braciuai 
behind the apices of the spirals. 
These external and internal peculiarities afford a sufficient basis for the sep¬ 
aration of shells of this type from Z. modesta and its allies. Mr. Billings de¬ 
scribed two varieties of A. Headi, viz., A. borealis, from Lake St. John and the 
Saguenay River; and A. Aniicostiensis, from Anticosti, both from the Hudson River 
formation. The former “ differs from the typical form in being more elongate- 
oval and in having a more tumid umbo” {op. cit., p. 147). This elongate variety 
prevails in the Hudson River fauna of Ohio, though in association with shells 
agreeing with the typical A. Headi. The variety Aniicostiensis retains more of 
the contour of a Zygospira, the pedicle-valve being more prominently keeled, 
the convexity more unequal, and, furthermore, there is a broad sinus on the 
brachial valve, while there is no trace of one on the other valve. This fossil is 
like Z. erratica, both in contour and in the fine striation of the exterior. If 
there is a specific difference in the two forms it is extremely slight, too slight^ 
indeed, with our present knowledge, to indicate either in words or illustration. 
These forms are interesting as being intermediary between the typical Zygospira 
and the representatives of the proposed subgenus Catazyga.* 
*Our specimens of Athyris Headi its variety A. Anticostiensis are from the oi-iginal localities, and 
from the investigation of these we are compelled to disagree with Mr. Davidson’s determinations given 
upon pages 126-128 of his Supplement to the British Brachiopoda. On page 127 he states that 
