HAI.ol-oDA. 779 



tn* htttMplfil-l 



upward t. 'niiin.it MID of the continuous siplional -In-nth, there is a sudden increase in 

 the depth of tlic aii -rhuml" 



Tin- marginal in -iilmiartfinal portion of the sipho explains the obliquity of the 

 >rptal animlations U|K)n tliis tube, and the gentle incurvature of the >cptal fimrirU. 

 the annuliition of this tube. There is nothing in the material in hand to indicate 

 any -- tMitial 'liitt'ifiirc-. fnMn the New York specimens of this species. 



Formation and locality. The majority <-f th< <>xamplrs examined are from tte Trenton llaieatoneof 

 Cannon Falls, Minnesota, and are from th- roll.vtiun of the late W. II. Sooflcld. Th<- large siphon floured 

 Is from the same horizon at WykofT, Minnesota (collection of Dr. C. H. Bobbin*), and other fragments 

 from Derorah, Iowa. 



CAMKROCKRAS HENNKIMNI, sp. nor. 



I'l.ATK Lit. KIOS. l-i; IT.ATK Mil Mc.~ 1-1. 



Tins a tine large species, the most complete of the fragments which represent 

 it indicating a length of not much less than four feet, with shell very gradually 

 expanding. In a distance of 230 mm. the transverse diameter increases from 94 to 

 100 mm. In section the shell is subelliptical being perceptibly flattened on the 

 siphonal side, and less so on the opposite side, while the lateral curves are compara- 

 tively narrow and abrupt. The air-chambers are relatively narrow, those exposed 

 averaging about 20 mm. in depth, without increasing in this respect toward the 

 upper extremity. There are fourteen of these chambers in a length of 270 mm. 



The sutures are not regular and simply transverse in their direction, but upon 

 the siphonal side make a broad retral curve along the median line, bending forward 

 again for one-third to one-half the depth of a chamber on the sides, but upon the 

 antisiphonal side being more directly transverse and without curvature. The septa 

 are very deep, sloping with broad, gently concave, almost, at times, plane surfaces 

 to the sipho, about which there is a constriction. The sipho is very large, measuring 

 46 mm. in diameter where the septum is 90 ram. In the lower portions of the 

 specimens a distinct and continuous siphonal sheath is retained. The vertical 

 section of a fragment represented on plate LIU, fig. 1, shows the thickness of the 

 siphonul wall, which has been preserved only on one side, the other having been 

 destroyed in the process of fossilization. It is here seen that the mode of union of 

 the septa to the sipho is .1 tirm adhesion of the former to the outer wall of the latter, 

 the septa being slightly thickened at their junction therewith. The structure of the 

 shell substance shows with clearness that however firm the coalescence of these parts 

 the distinction between the two is sharp. The specimen also shows the excent im- 

 position of the sipho, the shell not being much abraded on the siphonal side, but 

 having lost considerably on the other side. 



