. Bulletin - New York State Museum. Science. 220 NEW YORK STATE MUSEUM Genus aechmina Jones & Holl [Ety.: ar/!'j, point of a spear] {An. and mag. nat. hist. ser. 4. 3:217) Carapace with thick valves, straight at hinge line, rounded at the- ends, and convex at the ventral border. Surface drawn out into a broad-based and sharp pointed hollow cone, which either involves the whole surface, or rises from the postero-dorsal or centro-dorsal region. Aechmina spinosa (Hall) (Fig. 152). Cytherina spinosa Hall (1852. Pal. N. Y. 2:317, pi. 67) Distinguishing characters. Strong oblique spine^. thic
. Bulletin - New York State Museum. Science. 220 NEW YORK STATE MUSEUM Genus aechmina Jones & Holl [Ety.: ar/!'j, point of a spear] {An. and mag. nat. hist. ser. 4. 3:217) Carapace with thick valves, straight at hinge line, rounded at the- ends, and convex at the ventral border. Surface drawn out into a broad-based and sharp pointed hollow cone, which either involves the whole surface, or rises from the postero-dorsal or centro-dorsal region. Aechmina spinosa (Hall) (Fig. 152). Cytherina spinosa Hall (1852. Pal. N. Y. 2:317, pi. 67) Distinguishing characters. Strong oblique spine^. thick and hollow at the base, either elongate or short; pointed upward, outward and forward, and sometimes slightly bent; valves thickened on the free border by a raised, rounded but irregular mar- gin; area at base of spine hollow and smooth; raised margin sometimes punctate; spine often long and projecting beyond the upper margin of the valve. Found in weathered Rochester shale on the talus Fig. 152 Aechmina ^^ ^^'^^ Romc, Watcrtown and Ogdensburg railroad ^'^After^jones^^^^^^^ cut abovc Lcwistou. The valves are often im- bedded in the shale with the inner concave surfaces exposed. Alsa^ found at Lockport (Hall). Order TRILOBITA Burmeister The trilobites are extinct Crustacea, wholly confined to the Paleo- zoic seas. The body was covered with a carapace longitudinally divisible into three parts. The anterior portion comprises the head- shield, or ccphalon, which is usually semicircular, with a straight pos- terior border. The central of the three cephalic lobes is the glabella^ which is the most prominent part of the cephalon. It is of varying outline, and more or less divided by transverse furrows or pairs of furrows. The last furrow is the occipital furrozv, and delimits the occipital rm^, which is just anterior to the first segment of the thorax. On either side of the glabella is a pair of cheeks, divided by the facial siitnre into fixed cheeks (those next to the glabella) and
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectscience, bookyear1887
