BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 407 



or ventral saddle (sometimes absent when the siphuncle is sepa- 

 rated a little more from the outer wall, as on plate 2, figure i), 

 which is flanked on both sides by broad lobes, passing into still 

 broader saddles, which are separated by a low lobe approximately 

 opposite the siphuncle. 



Siphuncle tubular, of roundish oval section similar to that of 

 the conch, but as a rule flatter on the side next to the conch ; 

 very large, approximately one third the diameter of the conch ; 

 in contact with the latter and lying on the flatter side of its 

 ellipse. The surface is characteristically marked by strong 

 transverse ribs which on the outer or ventral side curve abruptly 

 upward on account of the direction of the septa, its apical part 

 projecting beyond the chambered shell for a distance of about 

 75 mm ; gradually expanding from the blunt apical end, which 

 here has a diameter of about 3 mm to 11. 5 mm at the begin- 

 ning of the phragmocone, where it contracts to 10 mm and 

 then gradually expands again. The anterior third, roughly 

 stated, of the siphuncle is empty (endosiphocylinder), the re- 

 mainder filled with calcite, containing the endosiphosheaths, which 

 like the endosiphocone possess an apical angle of not quite 20°. 

 The endosiphocone has a subtriangular section, one side of which 

 corresponds to the flatter side of the siphuncle. A conchiolinous 

 flattened tube (endosiphocoleon) proceeds apicad from the interior 

 of the endosiphocone. It attains a width of 10 mm behind the endo- 

 siphoconCj but gradually tapers to the width of the enclosed endo- 

 siphotube, becoming apicad more and more indistinct by a loss of 

 conchiolinous matter and replacement by organic calcite. The endo- 

 siphotube is a fine subcentral tube with conchiolinous walls, circular 

 section and a diameter not surpassing one half mm. It continues 

 to the apical end, diminishing slightly in diameter. The endosipho- 

 coleon and endosiphotube are suspended by three membranes (endo- 

 siphoblades) arranged like an inverted T. In some specimens a 

 longitudinal, strongly impressed (muscular?) line passes along the 

 outer wall directly above the siphuncle. 



Position and locality. Very common in the Fort Cassin beds at 

 Valcour, along the shore of Lake Champlain ( 2065 A., and A^ of 

 cur section) and also at Fort Cassin \'t. from where it was origi- 

 nally described. As a rule only the solid calcified apical portions 

 of the siphuncles are observed. 



Observations. Whitfield has assigned smaller orthoceracones 

 from Fort Cassin to Orthoceras explorator Billings, a 



