228 Report of the State Geologist. 



The Gonangium. 



Among the complete colonies of D. pristis^ Hall, found in the 

 shale, I happened to notice one of more than common interest. 

 It is a rather small specimen, the rhabdosomes of which are very- 

 short, but, although much compressed in the rock, it reveals all 

 details with remarkable clearness. Moreover, the chitinous sub- 

 stance remains on both slabs; the exact observation of each 

 detail can, therefore, be tested by the counterpart. 



This specimen, one-half of which is represented in PL I, fig. 5, 

 shows, besides five rhabdosomes and a very small central disc, 

 an oval group of siculge (g), all of which have their broad ends 

 directed outward. The proximal ends of the siculae radiate from 

 an axial club-shaped projection, which is surrounded by a groove. 

 The basal siculae are very distinct and well developed ; they make 

 their connection by thin hair-like processes, such as are observed 

 on well-preserved detached siculse. . Toward the distant end of 

 the group they become more crowded and apparently smaller. 

 On the siculae lies a thick oval chitinous ring, which forms the 

 margin on one side of the group, whereas, on the other side, it 

 overlies the siculae. It is apparently the remainder of the capsule 

 which inclosed the sicul^ and burst in becoming compressed, 

 allowing the siculse to be pressed out. 



There is no doubt that we have here an organ in which the 

 siculge originated, the details all being so clear that they can be 

 seen by the naked eye. After this discovery I searched all com- 

 pound fronds in my possession for these organs, and was rewarded 

 by finding them in numerous colonies, both of D, pristis^ Hall, 

 and of D. Ruedenianni^ Gurley. 



One of the best specimens observed is represented in PL I, 

 fig. 8. It is especially interesting, because the " gonangia," as 

 these organs are provisionally termed, are very large (they 

 have a diameter of 4 mm.) and because the fossil is not 

 so much compressed but preserved in relief. It is a compound 

 frond of D. pristis^ Hall, the rhabdosomes of which are mostly 

 crowded on one side. In a deep pit in the center, we notice the 

 base of the chitinous central disc with the funicle. Around 

 the central disc there are four, subcircular remains of gonangia, 

 which are as distinct as the rhabdosomes! In the center of 

 the gonangia, projecting on three sides, are round nodes, on 



