8 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



membraue in a sort of border or festoon Having afterwards submitted the 



minute shell to the action of water, accompanied by a little caustic potash, I was 

 able to isolate the brachial appendages without effecting any fracture. The calcareous 

 appendage, or loop, is formed at this stage of growth by two little short calcareous 

 processes only, which represent the origin of the crura and offer no traces either of the 

 principal stems or of the transverse connecting lamina of the loop. In this first stage, 

 the brachial appendages entirely resemble those of a Bhynchonella ; and if one limited 

 oneself to a superficial examination one would be more disposed to take the embryo of 

 Liothyris vitrea for a minute Rhynclionella, the then triangular aspect of the foramen 



and the pointed beak heightening the illusion I next examined diffei'ent 



examples of 6 and 7 millimetres in length ; the shell then, although still quite young, had 

 completely changed in aspect, its shape being essentially the same as in the adult condition. 



The loop occupies about a fourth of the length of the shell, and is complete in all 



its parts. I next examined specimens of 10 millimetres in length, in which the only 

 differences, and very sliglit ones, were limited to the loop being a little broader ante- 

 riorly, and it never afterwards assumed any difference Therefore the study 



of Liothyris vitrea offers three facts of great general importance, namely : — 



" 1. The brachial apparatus or loop follows in its development a regular progression. 

 It is at first as simple as possible, composed of two little branches which unite after- 

 wards so as to form a small apparatus in the shape of a crest. 



" 2. This apparatus once formed does not undergo any metamorphosis, and does not pass 

 thi'ough the complications that one observes in Terebratella. 



" 3. As soon as the labial appendages or arms have developed themselves, and the 

 brachial apparatus or loop has commenced to be formed, the mantle and the arms present 

 in the interior a very complicated system of calcareous spicula, especially destined to 

 protect the channel of circulation, whilst in the Terchratutcs with long loops, JFaldheimice, 

 and Terebratellce, one can discover not a trace of similar spicula." 



The soft parts of the animal of Liothyris vitrea are very similar to those of Tere- 

 hratulina caput-serpentis, to which we allude in the sequel. 



It is to be regretted that the anatomy of L. vitrea has not yet been published, and 

 still remains a desideratum. The intimate shell-structure of L. vitrea has been minutely 

 described and illustrated by Van Bemmelen in his memoir on the anatomy of the 

 Brachiopoda * ; tlie circular perforations, or canals, are widely separated from each other 

 (as may be seen in the figure) although very small on the surface of the shell itself. 

 Malformations in L. vitrea are not common. M. E. Deslongchamps has, however, 

 described and illustrated a very remarkable one (Plate I. fig. 10 of this work) in which 

 there exists a large longitudinal septum in both valves, which has been caused by an 

 accident similar to that which caused the formation of the hole in Terebratula diphya. 



Liothyris vitrea is a common fossil in the Pliocene rocks of Sicily, and occm's at 

 Trapani, Tremonte, Gravitelli, and also at Terreti, near Eeggio, in Calabria. 



The shell referred to L. vitrea, by Chemnitz, in his Neues Conch. Cab. p. 97, tab. 78, 



* Over den Bouw der SchcIpeiJ van Bracbiopoden en Cliitoucn, 18S2. 



