PALAEONTOLOGY. 39 



tudinally crested on the inside. The tubes in the massive or 

 laminar forms are prostrate, diverging from a central point, and 

 open obhquely to the surface ; in the ramose forms the tubes are 

 ascending and arching outward from an imaginary central axis, as 

 in branching forms of Favosites. Tube walls moderately stout 

 and not expanded at the orifices, the inner margin of which is 

 appressed to the body of the polyparium and lost in a common 

 interstitial surface ; the outer margin projects as a sharp lip. Cav- 

 ities of tubes lined with longitudinal crests or rows of spinulose 

 projections, which normally should be twelve in number, but it is 

 rarely the case that all of them are found developed. Usually two 

 or three of the crests, or crested rows of spinules, grow large and 

 conspicuous ; the others have a more rudimentar}' development. 

 or have sometimes become obsolete. Diaphragms comparatively 

 more distant and irregular than in Favosites. Pores x&ry large, sit- 

 uated on the two lateral edges of the compressed tubes, or at least 

 in close proximity to them. The genus Alveolites appears contem- 

 poraneously with Favosites, for the first time, in the upper Silurian 

 strata. 



ALVEOLITES XL\GARENSIS, X. Sp. 



Convex hemispherical masses of concentrically laminated structure, 

 covered by an epithecal crust on the lower concave side, or undose, 

 discoid expansions composed of superimposed layers of prostrate 

 tubes, diverging with a slight spiral twist from a central vertex, sev- 

 eral of which are sometimes observed on an expansion. The com- 

 pressed tubes are always more convex on the upper sides, with a 

 corresponding concavity of the lower sides, which rest on the con- 

 vexities of the subjacent tubes. The compression is sometimes 

 only moderate, and the outside of the oblique orifices is formed by 

 a projecting arched lip ; in other specimens the compression is 

 stronger, the orifices become narrow, lanceolate, or fissure-like, 

 with an appressed subplane lip on the outer side. The orifices of 

 the majority of specimens are surrounded by a cycle of denticules, 

 corresponding to longitudinal rows of spinules along the inner sur- 

 face of the tube walls. The rows are rarely fully twelve in num- 

 ber, and some of them are always more strongly developed than 

 others. In some specimens no denticulation of the orifices can be 



