Palaeozoic Bivalved Entomostraca. 183 



had come under my notice. Having expressed a difficulty* 

 in mastering the description of figures of the so-called " Cy- 

 pridinen," published in 1856 (' Beitr. Pal. Thiir. Waldes ') by 

 my friend Dr. Richter, of Saalfeld, I was most courteously 

 favoured by him with a good set of specimens for examination 

 early in 1874. Some, indeed, of these were types of species 

 published in 1869, in his paper on the Devonian Entomostraca 

 of Thuringiaf, which memoir had escaped my observation 

 until after my " Notes on Entomis" &c. were printed in 

 1873. In the meantime, before Dr. Richter's specimens 

 reached me, I was so much struck with the peculiarity of the 

 Entomostracan structures figured in the ' Zeitschrift ' of 1869, 

 that I could not but believe some peculiar generic form, oc- 

 curring in the Thuringian strata, had been elaborated by my 

 friend ; and I suggested, in the ' Neues Jahrbuch fur Min.' 

 &c. 1874, 2. Heft, p. 180, that his name should be associated 

 with it in the term Richteria. 



After a long study of Dr. Richter's specimens, having 

 taken them up again and again during the last four years, 

 as new information on analogous and collateral materials 

 become available, T cannot find any reason to support the 

 establishment of my proposed genus " Richteria ;" for the 

 typical specimens show merely the conformation and cha- 

 racters of Entomis ; and lately Dr. Richter has informed 

 me that he now refers his so-called "Cypridinen" to that 

 genus. 



Description. — Two separable valves, oblong-ovate in out- 

 line, ornamented with longitudinal and subconcentric riblets, 

 and impressed externally with a more or less pronounced 

 nuchal or dorsal furrow, ending in a small and often obscure 

 pit at about the middle of the valve, constitute the best pre- 

 served remains of the Devonian Entomides under notice. 



The pressure, both vertical and lateral, to which the Devo- 

 nian schists have been subjected very rarely leaves these little 

 fossils in their original shape ; and the material of the valves 

 has almost always disappeared, leaving hollow external moulds 

 and convex internal casts. The former show the delicate cos- 

 tulation of the valves ; the latter are usually smooth and rarely 

 bear any of the external ornament. Flattened by perpendi- 

 cular pressure, and lengthened, shortened, or otherwise dis- 

 torted by lateral pressure in different directions, the natural 

 ovate form is seldom preserved, but is replaced by every 

 modification from subcylindrical to circular and oblique-oval 



* Op. cit. p. 415, note. 



t 'Zeitschrift deutsch. geol. Gescllsch.' Jahrgaog L869, pp. 767-776, 

 pis. xx. & xxi. 



