76 ./. W. Jackson — The Brachiopod Liothyrella. 



etc. This featui'e is clearly shown in. Davidson's figures,' and is 

 referred to in tlie text (p. 54). It resembles that seen on recent 

 Dyscolim, especially D. crossei, I)av. 



Among the Tertiary species, T. lisimiata, from the London Claj', 

 is a good example. On my specimens from near Fareham the 

 radii are fairly wide apart and more noticeable on the side areas. 

 The dorsal valves show a thin, low, thread-like mesial septum, 

 superposed on a flat platform separating large pear-shaped muscular 

 impressions. In type of cardiualia tliis species is similar to the 

 well-known Crag Terehrahdce, which also show the striation very 

 distinctly, especially on the lateral parts of the valves. These, 

 however, have no mesial dorsal septum. They are presumed to be 

 true Terehratulce. The cardinalia of these Crag forms and of 

 T. bisinuata, of the London Clay, have never been properly described. 

 The type is a peculiar one : there is a prominent semicircular, or 

 semi-ovate, cardinal process standing out from the apex of the valve 

 like a shelf; the socket-ridges, bounding the dental sockets, are 

 prominent and diverge from the apex, or at least from the corners of 

 the cardinal process; their inner sides descend sharply and touch 

 the floor of the valve posteriorly ; the plates then curve upwards 

 (ventrally) to the well-marked crural bases, the posterior extremities 

 of wliich are often clearly separated from the apex by a small space. 

 On the inner sides of the strong ridges forming the crural bases, 

 thin, narrow, plates are given ofi', these plates being free from 

 contact with the valve posteriorly and well separated from each 

 other mesially.- In some of the dwarf Crag Terehratulce. these inner 

 hinge-plates are much broader and touch each other in the median 

 line at their posterior ends. "While dealing with the Crag Tere- 

 IratulcB it may be of interest to refer to an allied form occurring in 

 the Pliocene of Calabria, S. Italy. This form, usually recorded as 

 2\ grandis or T. scillce, has a type of cardinalia similar to the Crag 

 form, except that the inner hinge-plates are very rudimentary. Of 

 the flve examples cleaned out and examined (these being of equal 

 size to the Crag examples dealt with), all exhibit the same features ; 

 but in one or two there is a thread-like mesial septum. 



The above-mentioned ridges (crural bases) with their attached 

 inner hinge-plates clearly distinguish this type of cardinalia from 

 that of Liothyrma. No evidence of these inner plates is present in 

 any recent Liothyrinm ; nor are the crural bases so well defined. 



The ascription of the Chalk species to the genus Liothyrma 

 (mainly, I believe, on account of the grooves for the attachment of 

 the pallial sinuses showing through the test) is open to some 

 question. Their general external appearance, small foramen, and 

 the massiveness of the cardinalia suggest that they might be 

 terminal members of a distinct genetic group. The following 

 remarks are based mainly on a study of several valves of T. carnea 

 which have been developed to show interior details. The most 



^ Monog. Brit. Cret. Brach. (Pal. Soc), 1854, pi. v, ligs. 13-16. 

 " For a good figure of the cardinalia, see Davidson, Monog. Brit. Tcrt. Brach. 

 (Pal, Soc), 1852, pi. ii, fig. 3. 



