EAKLY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 57 



Genus HETERONEMA Ulrieh and Bassler. 



Heteronema Ulrich and Bassler, Smiths. Misc. Coll., vol. 45, 1904, p. 278. 

 Original description. — Zoaria, so far as known, consisting of usually simple, or 

 locally jointed, delicate, sparsely ramifying, tubular, creeping threads, arranged 

 without apparent order. Pores rarely observed, apparently always in a single row. 



Genotype. — Heteronema capillare Ulrich and Bassler. Silurian, isl- 

 and of Gothland. 



The species referred to this genus represent the simplest forms of 

 the Vinellidse and are distinguished from the type genus Vinella first 

 because of this extremely simple structure, but mainly on account 

 of the absence of the highly characteristic nuclei and consequent 

 radial arrangement of the threads. The following new species forms 

 such a regular network by dichotomous brandling that it must be 

 doubtfully referred to Heteronema. A species from the Upper Ordo- 

 vician (Maysville formation) of Ohio has a somewhat similar growth, 

 and it is possible that with more knowledge these two will be 

 referred to a new genus. H. priscum is of further interest in that 

 it is the oldest known bryozoan. The Ctenostomata are usually con- 

 sidered the simplest of bryozoans, and theoretically species of this 

 order should obtain in the oldest rocks. The discoveiy of such a 

 simple type of the order in the Cambrian is therefore in keeping with 

 our knowledge of the class. 



HETERONEMA PRISCUM, new species. 

 Text fig. 6. 



This species is founded on a number of specimens, all of wliich 

 consist of large or small patches incrusting the smooth shells of the 

 brachipod Oholus. It was at first believed that these incrustations 

 represented a reticulate surface ornamentation, but this view was 

 soon disproved by the different composition of the threads and 

 mainly by the fact that in some specimens one set of threads was 

 growing over another. 



The zoarium consists of thin, dark, corneo-calcareous threads bifur- 

 cating dichotomously so uniformly that a rather regular network 

 results. The individual meshes of this network average 0.4 mm. in 

 diameter, while the threads themselves are less than 0.02 mm. wide. 

 Frequently, as shown in figure 6 c, one zoarium may be noted grow- 

 ing over one or more previous incrustations. Upon examination 

 under a high power of the microscope small pores rather regularly 

 arranged are seen along the middle hne of the threads, while the 

 zoarial substance itself appears very faintly granulose. The threads 

 are not alw,ays of uniform diameter and occasionally are somewhat 

 bulbous. 



