602 



NEW YORK STATE MUSEUM 



and Lapwortli from the region along the south bank of the St Lawrence 

 from the Matane river eastward to Gaspe ; further, from Cape Breton island 

 and the St John basin by Matthew. In Europe D. f labellif or me 

 marks the last horizon of the Cambric in Esthonia, Russia; in the black 

 Alum shales of East and West Gothland, and of Scania; in the neigh- 

 borhood of Christiania, on Bornholm ; in the Lower Tremadoc of north and 

 south Wales, and in the county Meath in Ireland ; and at 

 several localities in Belgium. This form is at once the 

 longest knoAvn and thus far geologically oldest species of 

 the genus and has the widest distribution of the species of 

 Dictyonema. In distinction from the others, it appears 

 in the horizon, characterized by it, in immense numbers, 

 mostJy to the exclusion of other forms ; and the graceful 

 suspended bells have therefore, for a short time, swarmed 

 over a very vast tract of the northern Cambric ocean, in 

 immense multitudes. 



Development. The slates at Schaghticoke have 

 furnished a complete series of growth stages of D . f 1 a - 

 belliforme [pl.l, flg.1-20], the first one yet made 

 known of this genus. This permits the elucidation of a few facts. 



The youngest stage observed is a relatively short and stout sicula, 

 attached to an extremely long and slender nema [fig. 1]. By means of this 

 nema it was probably suspended from the beginning from a subcircular, 

 thinly chitinous organ, which is rarely observed [fig.lO] and which 

 may have been either a float or a membrane of adhesion to seaweeds etc. 



When the sicula has grown beyond the length attained in figure 1, a 

 lateral bud appears [fig. 2-4] which, after a short adherence to the sicula, 

 diverges under a very large angle (about 75°). This theca almost 

 immediately divides [fig. 5, 6j as it appears, both resulting thecae divei'ging 

 about equally. Next a third theca is noticed [fig.6, 7], all three being so 

 arranged as to form a tripod, and a fourth theca, apparently branching 

 from the third, quickly completes the original group of four thecae 



Fig. 27 Dictyonema 

 flabelliforme Eich- 

 wald (sp.) Fragment 

 showing dissepiment and 

 apertures of flanking 

 tubes. Schaghticoke. x5 



