REPORT ON THE RADIOLARIA. clxvii 



243. Mesozoic Radiolaria. From the Mesozoic or Secondary period numerous well- 

 preserved Eadiolaria have recently been described. They belong for the most part to 

 the Jurassic formation (see notes A, B, C), whilst the more recent Chalk (see note D) and 

 the older Trias (see note E) have hitherto yielded but few species. All the main divisions 

 of the Jura, both the upper (Malm) and the middle (Dogger), and especially the lower 

 (Lias) appear in certain localities to be very rich in well-preserved shells of fossil Poly- 

 cystina. Most of these are aggregated together in coprolites and quartzites (jasper, chert, 

 flint, &c., 248). The majority are Cy r toi de a, the minority Sphseroidea and 

 Discoidea in almost equal proportions ; a few Beloidea (Sphcerozoum) and 

 Phseocystina (Dictyocha) are also found among them. The general morphological 

 character of these Jurassic Radiolaria is very different from that of the nearly related 

 Tertiary and living forms. In general, their siliceous shells are firmer and more massive, 

 usually also somewhat larger, but of simpler structure. The manifold delicate append- 

 ages (spines, bristles, feet, wings, &c.) which are so richly developed in the living 

 SPUMELLARIA and NASSELLARIA, and are also well shown in the Tertiary species, are en- 

 tirely wanting in the majority of the Jurassic Polycystina. The Sphseroidea and 

 Prunoidea are all simple spherical or ellipsoidal lattice-shells (Monosphserida) ; con- 

 centric lattice-shells (Polysphserida) are entirely wanting. The Cyrtoidea are, for the 

 most part, devoid of radial processes or basal feet (Eradiata) ; triradiate and multiradiate 

 forms, such as are found abundantly in the recent and Tertiary formations, are very rare. 

 The large number of many-jointed forms (Stichocyrtida) and of Cyrtoidea with 

 latticed basal opening is very striking. 



A. The most important work on the Jurassic Eadiolaria, regarding which but little was known 

 prior to the year 1885, is the valuable and in some respects very interesting Beitriige zur Kenntniss 

 der fossilen Eadiolarien aus Gesteinen des Jura, by Dr. Eiist of Freiburg i. B. (1885, Palaeon- 

 tographica, Bd. xxxi. 51 pp. with 12 plates). Unfortunately this important work was issued only 

 when about half of the present Eeport was printed off, so that it was no longer possible to include the 

 234 species there described in its systematic part. I have therefore elsewhere given a list of the 

 Jurassic Eadiolaria, and at present only make the following remarks : Of the 234 species de- 

 scribed, the larger half (130) belong to the NASSELLARIA (Cyrtoidea), the smaller half (102) to 

 the SPUMELLARIA (38 Sphreroidea, 14 Prunoidea, and 50 D i s c o i d e a). In addition, 

 there are 2 PH.EODAKIA depicted, and several spicules which are probably to be referred to the 

 Beloidea. Among the 130 C y r t o i dea (of which 2 are described as Bo try odea), there 

 are 24 Monocyrtida, 14 Dicyrtida, 22 Tricyrtida, and 70 Stichocyrtida. Just as striking as the 

 predominant number of the last is the fact that there are only very few triradiate (9) and multi- 

 radiate (4) species found among these 130 Cyrtoidea, as also the large number of species with 

 latticed basal opening ; Step hoi dea appear to be entirely wanting. The rich material of 

 jasper, chert, flint, and coprolites in which Dr. Eiist found these Eadiolaria, is derived for the 

 most part from the Jurassic rocks of Germany (Hanover, South Bavaria), Tyrol, and Switzerland 

 (compare 248). 



