230 DR. T. DAVIDSON ON KECENT BEACHIOPODA. 



APPENDIX. 



The Anatomy of Crania from Dr. L. Joubin's " Recherches sur I'Anatomie des 

 Bracbiopocles Inarticules," Archives de Zoologie Experimentale, t. iv. p. 161, 

 1886. (Abstract.) 



Dr. L. Joubin dretlged Crania turbinata, Poli {—C. rostrata, Hoeningliaus), from a belt of calcareous 

 rocks about 200 metres from the shore, on the rocky coast of Banyuls-sur-Mer in the Eastern Pyrenees, 

 in depths varying from 50 to 60 metres. The specimens were generally covered with algae, and greatly 

 resembled in colour and form the objects to which they had attached themselves. He kept them alive 

 for six months and then preserved them in alcohol, as he was leaving the neighbourhood. Other 

 specimens were transferred to Roscoff and suffered no ill-eifects from the change of water, which differs 

 much from that of the Mediterranean ; later, they were again removed to Paris, and were still living 

 fourteen months after they had been dredged. The sjjecies exhibited great tenacity of life ; exposed to 

 sunlight without change of water for months together, neither extremes of heat nor cold, light nor darkness, 

 appeared to affect them in any way. Although the specimens obtained in November were full of ova, 

 no eggs were deposited during captivity, consequently it was impossible to trace the embryonic 

 development of the genus. 



In the course of exhaustive anatomical and histological investigations of this non-pedunculate 

 tretenterate Brachiopod with a wholly calcareous shell, Dr. Joubin recognizes the presence of two layers 

 in the structure of the hingeless shell, which is perforated by canals, the terminations of which in the 

 upper or free valve are arborescent, as described by Carpenter and King. The canals of the lower 

 and attached valve he shows to be irregular, slightly bifurcated, and non-arborescent in character. The 

 mantle lining the shells is so transparent as to be scarcely discernible. It adheres closely to the valves 

 and penetrates into the tubular perforations of the shell, and is permeated with yellow or whitish rami- 

 fications of a glandular aspect. These are the genital bands. The true colour of the mantle is slightly 

 green, due to special granulations contained in certain cells analogous to those of the red cells described 

 by M. Lacaze-Duthiers as present in Thecidium. The free portion of the mantle is covered with short 

 vibratile cilia, which cause incessant currents in the water admitted into the pallial cavity. Additional 

 currents are produced by the ruovements of the '' arms." The mantle is composed of a thin trans- 

 parent tissue, and the animal of Crania might almost be defined " as a layer of cartilaginous tissue 

 enclosed between two epithelia." The genitalia are contained in a fold of the mantle. The pallial 

 genital canals are from five to eight in number, uniting in one trunk on each side and for each valve, 

 and empty into the perivisceral cavity. The pallial cartilaginous tissue (" Stutzsubstance " of Van 

 Bemmelen) is thickest at the points of insertion of the muscles, where the shell-substance is not 

 perforated by canals. There are five pairs of muscles and an odd one. The mantle limits the size of 

 the visceral cavity, serves for the attachment of the muscles and of different membranes, and evidently 

 plays an important part in the respiratory processes and production of the shell. The cells of the 



