ATRYPA. 55 



little advanced, indenting that of the dorsal one. Surface of valves ornamented with nume- 

 rous small, radiating, rounded ribs, which continually augment towards the margin by the 

 means of bifurcation, or by the intercalation of ribs at various distances from the beaks. 

 The surface is also closely intersected or crossed by numerous foliacous expansions, in 

 the shape of plaited laminae or frills. Shell-structure fibrous and irnpunctate. Spiral 

 appendages, originating at the base of the socket-walls, form two large hollow cones 

 placed horizontally, with their apices directed inwards and towards the hollow of the 

 same (dorsal) valve, which they almost fill ; the inner sides of the spires are pressed toge- 

 ther and flattened, and with their terminations close to each other near the centre of the 

 bottom of the shell (PI. xi., figs. 7, 8). In the interior of the dorsal valve the quadruple 

 impressions of the adductor muscle are separated by a medio-longitudinal ridge, the 

 pedicle or dorsal adjuster muscles being probably fixed to the two small cardinal plates. 

 In the ventral valve, at the base of the teeth a semicircular ridge curves on each side, 

 forming a saucer-shaped depression, open in front, and into which the muscles were 

 fixed (PI. xi., fig. 9) ; the divaricator muscles seem to occupy the largest portion of the 

 depression, and to have been divided by an obscure mesial ridge ; beyond these, and at 

 a little higher up, are placed the pedicle muscular impressions, and above the mesial 

 ridge, nearer the beak, is seen the oval scar left by the adductor. The vascular impres- 

 sions on the dorsal valve consist of two principal trunks, originating on each side 

 between the cardinal and pedicle muscles ; these soon divide into two primary branches, 

 which extend right and left almost parallel to the margin, giving off at various intervals 

 smaller bifurcating veins, which are directed towards the edge of the shell. Proportions 

 very variable : 



Length 2 inches 5 lines, width 2 inches 2 lines, depth 1 inch 2 lines ; but the shell 

 has usually smaller dimensions. 



05s. At page 127 of Hanley's 'Ipsa Linnsea Conchylia' we find the following re- 

 marks : — " Anomia reticularis. In the Linnean collection are several specimens of this 

 fossil, which alone of those present — and its presence in his cabinet has been recorded by 

 our author — answers to the description in the ' Systema.' The species, which is well 

 known, and is found very abundantly in all the beds from the Devonian to nearly the 

 bottom of the Silurian system, has received the following appellations : 



" Anomitks reticularis, Wahlenberg, 'Nov. Act. Soc. Upsal.,' vol. viii, p. 65. 



" Terebratulites priscus, Schlotheim, ' Petrefact.,' pi. lxxxvii, fig. 9. 



" Terebratcla affinis, Sowerby, ' Min. Cone.,' pi. 324, fig. 2. 

 " &c, &c. 



" The name of reticularis, being traced back to Linnaeus, must henceforth be adopted 

 to the exclusion of the many others it has received. (Sharpe, MS.)" 



In this statement I am fully prepared to coincide, having also carefully studied the 

 Linnean specimens in company with MM. Bouchard and Salter. 



It is a most variable shell, and has, consequently, been shifted about from genus to 



