322 GENERAL SUMMARY TO 



kidney-shaped. They are supposed by Hancock to escape by two orifices situated at the 

 sides of the mouth. Recent Biscina often seem to have minute fry attached to their 

 valves 3 and Prof. Suess, of Vienna, has noticed a specimen of the fossil Stringoccphalus 

 which contained numerous embryo shells. 



As already stated, it is very often possible to trace the position of the ovarian spaces on 

 the interior surface of the valves of many fossil specimens of Brachiopoda, and 

 especially so in Orthis, Strophomena, and Productus ; and of these I have given good 

 illustrations. 



Before concluding this very brief account of the mantle of the Brachiopoda, it must 

 be remarked that in 1854, in his review of my Monograph ' On British Fossil Brachio- 

 poda,' Oscar Schmidt called attention to an important anatomical omission, namely, the 

 existence of a vast number of microscopic, flattened, calcareous, denticulated plates or 

 spicula on certain parts of the surface of the mantle, which served no doubt to stiffen 

 portions that contained them. 1 



It was moreover remarked, by Hancock and E. Deslongchamps, 9 that these calcareous 

 plates " are not spread over the entire surface of the mantle, but only over the large 

 vascular sinuses, the arms, and perivisceral cavity." These spicula do not, however, 

 appear to be present in every species, being totally absent in Lingula, Rhynchonclla, and 

 some other genera; but Deslongchamps again observes "After examination of the genera 

 Terebrati'Ia, Terebratulina, Megerlea, Kraussbm, and Platidia, we find a series in which 

 the number and consistency of the calcareous portions increase in a very rapid manner, 

 the spicula forming several layers, leading the observer by a series of gradations to the 

 genus Thecidium, in which the spicula are soldered together, occupying the whole of the 

 mantle, and incrusting it to such an extent that the mantle is no longer distinguished 

 from the shell itself. The mantle forms that calcareous mass which equals in consistency 

 the brachial appendages, a fact of which Palaeontologists have often and in vain sought 

 the explanation." 



Muscles. — In the General Introduction to Vol. I of this Monograph, Sir Richard 

 Owen described the muscles of the Brachiopod ; and in my portion of the same Introduc- 

 tion I reproduced some of Hancock's and my own views upon the subject. Since then 



1 In vol. xvi, 2nd series, of the ' Annals and Mag. of Natural History ' for December, 1855, I gave a 

 translation of the following passage from Prof. Schmidt's paper : — " The mantle, oral arms, and cirri in 

 Terebratulina caput -serpentis contain an innumerable number of calcareous plates, generally flattened, 

 dilated, and irregularly denticulated, situated in close vicinity to each other. It is easily conceived that 

 these calcareous masses stiffen the parts which contain them, and seem particularly to serve this function 

 in the hollow cirri, thus preventing their sides from sinking down. In the Norwegian Terebratulce I have 

 examined they are not to be found, nor have I obtained them in Terebratula dorsata ; but further investi- 

 gations conducted on a large number of species will show whether they are or are not peculiar to 

 Terebratula cc/put-serpentis." 



2 ' Sur la Fonction des Spicules renfermes dans le Manteau de certaines Brachiopodes,' I860, and 

 ' Rccherches sur 1'Organisation du Manteau chez les Brachiopodes articules,' 4to., Caen, 1864 



