648 CAMBRIAN BRACHIOPODA. 



Acrotliele Tnatihewi (Hartt), Grabau and Shimer (in part), 1907, North American Index Fossils, vol. 1, p. 200, fig. 234f 

 (not 234g). (Described. Fig. 234f is copied from Matthew, 1886, PL V, fig. 15; fig. 234g from Matthew's figure, 

 1895a, PL V, figs. Jar-h, of Acrothele matthewi prima, now referred to Acrotheh prima.) 



General form subcircular to transversely broad ovate in outline, with the posterior margin 

 slightly transverse. Ventral valve subconical in young shells, becoming depressed, with an 

 elevated apex in the adult stages of growth. The apex is within the posterior fourth of the 

 valve, usually about one-sixth the distance from the posterior to the front margins; it is 

 formed of two minute, more or less elongated tubercles, with a depression between them at 

 the posterior end of which a minute pedicle opening occurs; a specimen of the variety Acro- 

 thele matthewi multicosta Matthew shows a minute tubercle just back of the pedicle opening 

 that looks as though it were part of a ring that formerly extended about the apex, the two 

 side tubercles being other portions of the ring. A narrow false area is indicated on some shells; 

 on others it is absent. 



Dorsal valve slightly convex on the umbo, and nearly flat over the anterior portions; 

 apex marginal as far as can be determined from the compressed shells. The exterior surface 

 is marked by concentric hnes and strise of growth and a few laminated ridges near the outer 

 margins; on some specimens of the ventral valve one or two low, obscure ridges extend forward 

 from the apex to the front margin. The epidermal layer is also marked by fine granulations 

 or papillse that are thickly placed over the surface; on the outer portions the granules are 

 closely spaced on the top of low, irregular, narrow ridges in the same manner as on Acrothele 

 coriacea Linnarsson; the inner layers of the shell are shiny and marked by concentric lines 

 and very fine radiating strise. 



The shell is corneous and built up of several thin layers or lamellae. A large ventral 

 valve has a length of 7 mm. with a width of 8 mm. 



The interior of the ventral valve shows an apical callosity penetrated by the pedicle open- 

 ing, and back of it the base of the main vascular sinuses ; the latter extend outward and forward 

 to about the transverse center of the valve, and then forward, curving inward more or less; 

 rather strong lateral branches extend outward at varying points; one specimen shows three 

 branches and another seven branches; back of the base of the sinuses a narrow, depressed 

 space extends to the margin of a very narrow area; these features are shown in a cast of the 

 interior (PL LXI, fig. Ic); the median depressed space corresponds to the false pedicle furrow 

 in some species of Acrotreta (PI. LXV, figs. 3g, 3h). The interior of the dorsal valve has a 

 very characteristic median septum that extends forward from one-fourth to one-half the 

 length of the valve; also the posterior portions of the main vascular sinuses that originate 

 in front of the beak and extend outward and then obhquely forward. 



Of the muscle scars only the minute umbonal scars of the ventral valve have been observed; 

 these are minute and close to the anterior end of the false pedicle furrow. 



Observations. — In general form and size Acrothele matthewi is allied to A. coriacea Lin- 

 narsson. The interiors of the valves are also much alike, as may be seen by comparing Plate 

 LYI, figures la-c, with Plate LXI, figures Ic and Id (ventral valves), and Plate LVI, figure 

 le, with Plate LXI, figure Ig (dorsal valves). The main vascular sinuses of the ventral valve 

 of A. matthewi are stronger than those of A. coriacea, and the outer, granular surface of the 

 epidermal layer is also much coarser. Acrothele matthewi differs from Acrothele (Redlichella) 

 granulata (Linnarsson) in its smaller size and in the markings on the interior of the ventral 

 valve; the granulated outer surface of the two species is similar, the differences between them 

 not being greater than the variations on different portions of the same shell. From A. avia 

 Matthew and A. proles Matthew this species is separated by the surface characters. It is 

 difficult to institute detailed comparisons of outline and form of A. matthem and other species, 

 as both it and its varieties are represented by compressed and more or less distorted shells. 



Acrothele matthewi is a variable species, and Matthew has proposed subspecific names for 

 the most marked of the varieties. One variety (A. matthewi eryx) is recognized and named 

 from China. A large form in Matthew's collection labeled "Acrothele cf. granulata" appears 



