380 TWENTIETH REPORT ON THE STATE CABINET. 



This structure would give the simplest form of Khodocrinus, to which 

 genus I have provisionally referred the species. 



On the other hand, should the fossil prove to possess but three basal 

 plates, we have the structure of Actinocrinus, with a single series of 

 interradials, and the absence of an anal series. The regularity of its 

 structure above the base precludes its admission among ordinary cystidians ; 

 while with our present knowledge and insufficient material, I hesitate to 

 found upon it a distinct genus. 



GENUS HOLOCYSTIT.es (Hall). 



I had overlooked the fact that the name Holocystis had been proposed by 

 Lonsdale for a genus of corals. The difference of the terminal syllable 

 has in many cases been regarded as a sufficient distinction, and is per- 

 haps preferable to adopting a new name. Should it be objected to, how- 

 ever, I propose the name Megacystites. 



ORTHOCERAS LOXIAS (n.s.). 



PLATE 19 (10), FIG. 7. 



Shell of medium size, elongate, somewhat rapidly enlarging from the 

 apex ; section circular ; siphuncle central, or sub-central, scarcely con- 

 stricted at the junction of the septa ; septa distant about one-fourth the 

 diameter : chamber of habitation unknown. 

 Surface marked by sharply angular longitudinal carinse with regularly con- 

 cave interspaces, which, on the larger part of the shell, are distant fully 

 three sixteenths of an inch and gradually converge towards the apex. 

 The shell is silicified so that the finer markings are obscured, but there 

 are indistinct transverse striae crossing the spaces between the ridges. 

 No fine longitudinal striae have been observed, though they may have 

 existed on the shell in its original condition. 



The similarity of this species to O. columnare is obvious, but it tapers 

 more rapidly, and the septa are more distant. The length of the specimen 

 figured is about eight and a half inches. 



The species has been illustrated in this connexion from its general exter- 

 nal similarity to figs. 4, 6, 8 and 9, and from a belief, originally, that it 

 was from the same horizon, or not far removed therefrom. The specimen 

 has been a long time in my possession, and was obtained in the northwestern 

 lake region many years since, but I have no means of ascertaining the 

 particular locality. The weathered surface of the limestone has the aspect 

 of the Niagara limestone ; but the fresh fracture more resembles some 

 beds of the Clinton group in the vicinity of Green-bay. A critical exami- 

 nation of the rock, the nature of the crystalline filling of some of the 

 cavities, together with the silicification of the exterior shell and the prin- 

 cipal part of the interior, septa, etc., induces me to refer the species, with 

 some hesitation, to Lower Silurian age. 



