410 Mr. T. Davidson on the Brachiopoda. 



and ovaria resemble each other; the zoosperms are in the shape 

 of a thread with a small head (fig. 10). Prof. Owen was likewise 

 able to observe the first commencement of the development of 

 the ova in the Lingula (fig. 15) ; the embryos, first of an ellip- 

 tical shape, form a stem a little later, without any change 

 having been effected in the ulterior organization or develop- 

 ment. The embryos of the said Terehratula differ from this 

 very considerably (fig. 11) ; they resemble a Euastrum com- 

 posed of two unequal halves (for instance, the E. gemmatum or 

 ansatum, Focke) ; the rounded portion seems to be the anterior ; 

 the posterior part is a little wider, and is prolonged into two 

 points. What is the following development ? In none of the 

 ovaries observed by myself— for it is there that the embryo is 

 found— was the development more perfect. Considering our 

 total ignorance relative to the development of Terehratula, every 

 observation must prove acceptable.'^ 



4. On certain calcareous Plates found in the mantle , oral arms, 

 and cirri of Terebratulina caput-serpentis. 



In the same paper, Prof. Schmidt observes, " that 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, as seen in the examples figs. 12, 13 & 14. It is 

 easily conceived that these calcareous masses stiffen the parts 

 which contain them, and seem particularly to serve this func- 

 tion in the hollow cirri, thus preventing their sides from sinking 

 down. In the Norwegian Terehratula I examined they are not 

 to be found, nor have I obtained any in Terehratella dorsata; 

 but further investigation conducted on a larger number of 

 species will show whether they are or are not peculiar to the T. 

 caput-serpentis" 



We may here mention that M. E. Deslongchamps has ob- 

 served a somewhat similar occurrence in his new species of Mor^ 

 risia, for we find stated in a note he has added to my description 

 of Morrisia (French edition) : " Having placed in water during 

 several hours a Morrisia, which contained in its larger valve a 

 portion of its cirriferous arms, as well as their desiccated mem- 

 brane, we were able, after their immersion, to extend them more 

 than before : in placing these remnants under the microscope 

 we saw that they contained irregular scattered granulations 



to M. Loven, are the Ter. (Rhynchonella)/?s^Y^acea, T. caput-serpentis, T. 

 cranium, and T. septigera. Mine answers better to T. septigera than to 

 the others, bnt it doea not possess the characteristic septum in the smaller 

 valve." 



