CEPHALOPODA. 301 



factory determination, has been referred to on page 265, under the notice of 

 the distribution of species in the Upper Helderberg limestones. 



Formation and localities. In the calcareous shales of the Hamilton group, at 

 Geneseo, Livingston county ; on the shores of Seneca lake ; and in the coarser 

 shales east of Cayuga lake, New York. 



Orthoceras Sicinus, n. sp. 



PLATE XXXVIII, FIGS. 1, 2. 



Orthoceras subulatum, Hall (in part). Illustrations of Devonian Fossils : Cephalopoda. Explanation of 



plate 38, figs. 1, 2. 1876. 



Shell straight, regularly enlarging. Transverse section subcircular. Apical 

 angle 8° in a specimen slightly compressed. Initial extremity unknown. 



Chamber of habitation, air-chambers, septa and siphuncle not observed ; 

 owing to the test covering the entire surface of the tube, and the apical 

 portion being compressed. 



Test thin. Tube ornamented by regular low, rounded annulations, or 

 transverse undulations, of wbich there are about seven in the length of ten 

 mm. Surface reticulated with fine sharp, transverse and longitudinal striae 

 of similar character. 



The specimen figured has a length of sixty mm. with diameters of fifteen and 

 seven mm. at the two extremities, and shows about thirty-five annulations. 



This species is distinguished by the low annulations of the tube, and reticu- 

 late surface. In its general appearance it somewhat resembles 0. subulatum, and 

 occurs in the same association ; but that species has a smooth, or fine trans- 

 versely striate surface. A closer resemblance is found with 0. textum ; but 

 the annulations are not present in that species, and the reticulations of the 

 surface are finer and more irregular. It is distinguished from the other 

 annulated forms, here described, by its surface characters and the low, 

 rounded, sometimes obsolescent annulations. 



Formation and locality. In the carbonaceous beds of the Marcellus shales at 

 Schoharie, N. Y. 



