Spkciks of thk CiiEMrNo Gitoiri'. 145 



the surface can be made out on nearly all examples, but it is not such as to 

 give a clew to the skeletal structure, except as we may infer that the skeleton 

 was fine and dense, and we know that the nodes were tufted. 



A symmetrical individual of suboval outline has a length of 155 mm. and 

 a median diameter of 90 mm.; this is about the average size of most of the 

 specimens. 



Geological Iwrizon. In the Chemung sandstones near Cohocton and 

 Avoca, Steuben county, and at Lyndon, Cattaraugus county, N. Y. Named for 

 the late Reverend Jonathan Allen, former President of Alfred University, 

 Alfred, N. Y. 



AGLITHODICTYA, gen. nov. 



Small, button-shaped sponges, greatly expanded horizontally at mid-length, 

 abruptly tapering to both extremities. Aperture narrow ; surface finely retic- 

 ulate, without nodes or other ornament. 



Type, Aglitliodictya numuhna, sp. nov, 



Aglithodiotya numulina, sp. nov. 



Plate xxv, Figs 6-9. 



Sponge small, subdiscoidal, biconvex with reference to a median horizontal 

 plane, the parts below and above this plane being subconical, that above being 

 considerably the more depressed. Radical portion of the cup not fully retained ; 

 lateral expansion from the inferior extremity about thrice the vertical growth. 

 The sponge attains its greatest diameter at a horizontal plane lying about three- 

 fourths of the vertical distance from the inferior extremity to the aperture, 

 and is thence bent sharply ujjwards. Upon the matrix there is some trace of 

 an erect spicular lamella or expansion about the cup at this plane ; otherwise 

 the surface is smooth. The margin of the apertural orifice is rounded and 

 somewhat swollen into low irregular nodes. Departing from the orifice and 

 traversing the apertural slope to the peripheral angulation are traces of diver- 

 gent surface grooves or canals such as are frequent among the lithistid 

 sponges and are not unknown among the thick-walled hexactinelliils. 



The reticulum is exceedingly fine, but distinguishable over all of the 

 principal exposures of the surface. There is no noticeable predominance of 

 any spicular bands, and the quadrules are rather too indistinct to be accurately 

 measured. The species is based on a single fairly preserved specimen in a 

 . sandstone matrix ; the. form is well retained and the skeleton in the usual con- 

 dition of other sponges of this fauna. This specimen has a vertical length of 

 11 mm., a greatest diameter of 24 mm., and an apertural width of 8 mm. 



