A very striking feature of the biota of the Devonian as represented in the state of New York is the extraordinary development in its late stage, the Chemung period, of its silicious hexactinellid sponges. At various levels in the sandy deposits of this time they are found, sometimes as scattered individuals and sometimes in plantations of uncounted numbers, so that it is safe to say that from the bottom of the formation in the "southern tier" of counties to near its summit, the hexactinellids of this order, the Dictyospongida, are many times more abundantly represented than in all the rest of the world together. In their extensive monograph of these sponges Hall and Clarke ascribe seventy-seven species in sixteen genera to this formation within the borders of New York and the same rocks in northern Pennsylvania. Clarke has described a number of additional Chemung species, so that there are now about ninety outstanding specific designations for this Devonian assemblage. Sometime it will be a subject for discussion among morphologists whether this so-called order, Dictyospongida, is homogeneously constituted; probably it is not, but so seldom is the spicular structure retained in the sandy matrix that on the basis of general form and habit, and the arrangement of the spicular bands which are usually sharply preserved in impressions, all the sponge occurrences in this formation and those of like composition in the Mississippian faunas of Ohio and Indiana are now for convenience put in this single group. That they are for the most part accurately referred to the hexactinellids is abundantly shown by the spicular structure of the Mississippian species which has been demonstrated. The described species and genera have been established with the best