228 REPORT ON THE STATE CABINET. 



In Retiolites, where there is no well-marked division limiting the 

 common body, the union of the cellules with it is not so well defined ; 

 nor does there appear to be, in these forms, a continuous cell-partition: 

 the cellules open in a quadrangular aperture, which is a little oblique to 

 the transverse diameter. 



In those Graptolites with the simple transversely-oval orifices in the 

 test, as G. hiconiis, the arrangement of the common body and the commu- 

 nication of the cellules differ from all the other forms. There is an 

 apparent double communication with the common body, giving not only 

 the usual bilateral arrangement of the parts generally, but a bilateral 

 arrangement of the parts in the individual alveoles. 



The external orifice of the cellule in Graptolites is extremely variable 

 in form, and in its relative direction to the body of the cellule and to 

 that of the general axis. In a large proportion of the species, the aper- 

 ture is oblique to the axis of the cellule, a little expanded, and thickened 

 at the margin. The lower or posterior edge is often prolonged into a 

 mucronate point or expansion. This feature, combined with the various 

 degrees of curvature at or near the aperture, produces a great diversity 

 of external expression in the orifice. 



In G. nitidus and G, extensus, Plate iii, the plane of the orifice is nearly 

 rectangular to the axis of the cellule ; while in G. lifidus and G. penna- 

 tidus and others, the margin is produced into a strong mucronate exten- 

 sion. In G. octobrachiatus , the line of the cell-margin makes an angle of 

 more than 90° with the axis of the cellule. 



In mature individuals of G. clintonensis the upper part of the cellule is 

 recurved, and the orifice opens downward nearly at right angles to the 

 general axis, having a slight spreading and thickening of the border. In 

 less mature individuals the orifice is apparently angular, and opens 

 upward, while the plane of the aperture makes less than a right angle 

 with the direction of the general axis. It would appear that in the 

 progress of growth the cell-walls are continued, gradually contracting 

 above, and, after becoming free from the adjacent cellule, form a slender 

 gradually curving tube, which, in mature individuals has its orifice 

 directed backward. 



In Dendrograptus, the form of the orifice and outline of the aperture 

 present variations similar to those of the simple uniserrate Graptolites ; 

 but some species show modifications in the form of the cellule which do 

 not accord with the more simple species of the genus. In Dicttonema, 

 the cellules are not fully known ; the orifices are marked by a prominent 



