28 CRETACEOUS PELECYPODA 



Deshayes brings in support of his unity of Lamarck's Clavagella some 

 fossil species, saying that the usual triangular shape of the valves of the recent 

 Bryopa is connected with the characters of what has here been called Clavagella. 

 This is, as regards the form of the valves, quite correct; the triangular shape 

 passes gradually into an oval, but the shape of the valves ]>as, strictly speaking, not 

 been considered as one of the striking distinctions of Bryopa. Sandberger 

 (Mainzer Beeken, pi. 21, fig. 3,) figures such a Clavagella in which the valves 

 are intermediate in shape between those of other fossil Clavagellce and the recent 

 Bryopa, but it distinctly secretes tubuli on the mantle edges like the former, and 

 its habitat also corresponds with it. The known fossil Clavagella; generally bore 

 in shells, or near the surface of corals, having the ventral side, where the longest 

 tubuli are formed, free. Very often these tubuli are found secreted all roimd the 

 edge of the mantle, that is, along the margins of each valve ; this is probably more 

 commonly the case in such species as bore in sand, than in those which attack 

 shells. The largest number of the fossil species belong to Clavagella, as restricted. 

 In the third form for which I have proposed the name StirpuUna, and which 

 is represented by the well known fossil species Sthp. (Clavagella) coronuia or 

 hacillaris of Deshayes, the tubes are closed in front, the diaphragm being 

 perforated about the middle by a narrow slit, and at the edges suiTounded by 

 numerous irregular tubuli. The valves are subequal, the left being usually the 

 smaller one ; the tube is very similar to that of Brechites, and the species, like 

 those of the last named genus, lived in sand. It even appears difficult in some 

 fossil species to ascertain, whether only one or both of the valves were attached to 

 the tube, thus indicating an intimate connection between the fossil StirpuUna 

 and the recent forms of Brechites. I shall subsequently mention the repre- 

 sentatives of this sub-family recorded as occurring in cretaceous deposits. 



c. Sub-family,— BRECHITIN^. 

 (See H. aud A. Adams, Gen. ii, pp. 649-650). 



Both valves grown together with the tube, the anterior base of which is pro- 

 vided with tubuli, usually arranged in a fringe round the disc, being more or 

 less perforated and possessing a sub-central narrow fissure. 



8. Humphreya, Gray, 1858. Tube irregular, attached to foreign objects with 

 its anterior ventral termination ; but two specimens of the only species, S. Strangei, 

 have as yet been found, and it has not been ascertained whether their growth is 

 normal or abnormal ; the latter is more likely the case. 



9. Brechites, Guettard, 1771, {Asptergillum auctorum). Vah-es on the tube 

 considerably exposed, their outlines distinctly marked ; posterior end of the tube 

 simple. 



9a. Warnea, Gray, 1858. Posterior end of tube fringed, otherwise as in 

 Brechites. 



