No. 186.] 27 



Genus Trematospira (Hall, 1857). 



Spirifer : Conead, Hall; jitrypa : Hall. 

 [ G-r. rgsfia, foramen ; aTteiQU, spira.} 



Shell transverse, elliptical or subrhomboidal, inequivalve, furnished 

 with internal spires (arranged as in Spirifer) : hinge-line shorter 

 than the width of the shellj cardinal angles rounded. Valves ar- 

 ticulated by teeth and sockets : beak of ventral valve produced 

 or incurved and truncated by a small round perforation, separated 

 from the hinge-line by a deltidium. A deep triangular pit, or 

 foramen beneath the beak of the ventral valve, which is filled by 

 the closely incurved beak of the dorsal valve. False area some- 

 times defined. 

 Surface marked either with strong simple plications or finer fasci- 

 culate or bifurcating strise, which cover also the mesial elevation 

 and depression. Shell structure punctate? 



In the extension of the hinge-line, the mesial sinus, the internal spires, 

 and, partially, in the exterior markings, this genus resembles Spirifer 

 and Spiriperina : in the perforate beak, false area, and incurvature of the 

 beak of the dorsal valve beneath the apex of the opposite valve, it resem- 

 bles Atrtpa ; while one of the species has the general aspect of Rhtn- 

 CHONELLA. From Retzi^, Spirigera, and Merista, which have similar 

 internal spires, it is separated by external and other important characters. 

 The appearance of an area is deceptive ; depending mainly upon a partial 

 displacement of the valves, which presents to view the hinge-line of the 

 ventral valve. This is true of T. multistriata, where we find some speci- 

 mens with an appearance of an area, and others without. The T. perforata 

 is clearly without an area, as well as T. costata ; though the margin of the 

 foramen in the former of these is often defined in such a manner as to re- 

 semble a true area. The broad triangular foramen or pit for the reception 

 of the beak of the dorsal valve is a constant and conspicuous feature. This 

 pit does not appear to be like the foramen of Spirifer, an opening into 

 the cavity of the valve, but is spoonshaped, somewhat like that of Pen- 

 tamerus ; its lateral walls in T. multistriata having been traced for some 

 distance below the margins, apparently converging towards each other. 



The known species present the variety of surface marking, respectively, 

 of simple costae, strong angular striai in fascicles, and finer somewhat 

 rounded bifurcating or simple striae. Specimens of each are rare ; and of 

 T. costata, but a single one was found among collections continued un- 

 interruptedly through a period of ten years, and a second specimen has 

 since been obtained. The condition of the specimens is such as not to admit 

 of satisfactory investigations of the interior, which must for the present 

 remain partially undetermined. 



